So I already new the IR's were there and had played with them before using just the straight line in on my interface with some of the TH2 heads. For that stuff I found that the IRs weren't all that necessary for a good tone.
 
However over the past 6 months I've been playing around more with my outboard gear. I have a couple amps that have XLR line outs and a nice old American Mackie mixer. I can't really crank the amps up and mic them because a) I would get booted out of my apartment and b) my mics/room are/is crap so it would be a lot of effort for probably crap results.
 
So the line/inst in on the interface, although better than my old interface, is still just an all purpose hi-z with all the flaws that usually come with that. Using the line outs on the amps produces much nicer clean tones for sims but I've also started pulling out my pedals and recording distorted signals. I send all this into the Mackie mixer then to the interface and into Sonar.
 
The problem was with the pre distorted signals they were really chunky and saturated but they were just too squonky and in your face. It's just too darned "close" of a source so I'd have to keep those signals down in the mix and use them just to add some grit in the background.
 
I figured the missing piece of the puzzle was a cabinet and a bit of room reverberations. After dragging my butt on doing this experiment I just now tossed an instance of TH2 into the buss being fed by two of the pre distorted tracks (which are actually just clones of the same comp I made). I removed everything else except the cabinet and changed it to the IR cabinet(s) option.
 
Now at first I got confused and had tossed in TH2 Producer instead of the full version of TH2 (which I own and it is awesome) and was wondering why the heck I had so few cabinet options. Still though the few that were there immediately turned my ultra squonky, distorted line input into a much more relaistic and natural tone. EXCELLENT!! It wasn't EXACTLY what I wanted but it was workable.
 
Once I relaized my mistake about TH2 Producer vs. the full version I swapped it out for an instance of the full version and BAM... a whole buttload of new cabs were available with tons of difference micing options for each. Even in the first cab in the list I've already got the tone sounding just brilliant just by cruisng around the micing options and blending between the A and B cabs.
 
This solves a MASSIVE problem for me because now I get the benefit of using my amps which have proper guitar preamps (as opposed to interface Hi-Z or other not so great silliness), using my pedal collection which sound better than their sim counterparts (and I know how to dial them in from years of stage use) and get rid of that squonky "WAY TOO CLOSE!!!" sound that recording the line outs on the amps always causes.
 
Seriously it sounds just like my amps would pushing air and I don't have to endlessly fiddle around with amp sims dialing in tones (although TH2 does that really well anyway... I just like this way better because ultra high gain sim distortion just never seems quite right).
 
So yeah... have an amp you like with a line out but don't want to mic it or crank it up? Just record the line out and toss an instance of TH2 with ONLY the IR cab (remove everything else in the chain... especially the head(s)). Even TH2 Producer (the one that comes with Sonar X series Producer) has some useable cab IRs AND you can import your own if you want. Pretty slick.
 
Cheers.
 
 

If you are really happy with this approach, consider getting the Redwirez BigBox - all the IRs you could ever need and it comes with a small VST utility just for mixing IRs. I think Scook once recommended it to me. It was a really cool buy since it gives you a ton of versatile cab options that work with many sims.

Also, thanks for the tip! I've always hesitated buying an amp because my home studio situation is like yours. Sounds like it might be worth getting just a guitar preamp after all!

Sanderxpander
If you are really happy with this approach, consider getting the Redwirez BigBox - all the IRs you could ever need and it comes with a small VST utility just for mixing IRs. I think Scook once recommended it to me. It was a really cool buy since it gives you a ton of versatile cab options that work with many sims.

Personally, I am NOT a fan of RedWirez IRs. There's lots of good/great/awesome free IRs out there, and even some you can buy, other than Red Wirez.
 
TH2....I bought this a couple of years ago. It's a very underrated amp sim that should get more praise. It's easily one of the best. However, Revalver 4 and Recabinet 4 have come out since I got TH2 and those kind of trump TH2, especially Recabinet 4.

Sanderxpander
Also, thanks for the tip! I've always hesitated buying an amp because my home studio situation is like yours. Sounds like it might be worth getting just a guitar preamp after all!

Really I think the important part is just the preamp section but more specifically the transistor (or whatever it is) that responds to a guitar input properly. That's what things like the Z-Box and various DI thingies emulate. So you may not need a whole amp. Maybe just something like one of those Line6 pods but I don't know much about those. I'm assuming they are just like my Line6 Duoverb without all the power amp stuff to feed cabinets. Also my Duoverb is one of their earliest creations so they've come a loooong way since then. It's still a very handy amp.
 
However I'm really diggin' the line output from my 60's-70's era Traynor TS 140. It's a great sounding old transistor amp with a lot of really advanced stuff for the era (like a five band graphic EQ on top of the regular Tone, Mid, Bass knobs), sweet sounding, gain, boost and bright stuff, two channels (so I could actually do a duet with another player on it), pedal controller (which I don't own but I don't think that stuff was very common back then) and of course the XLR line out (as well as 1/4" line out). It's a combo but the cabinet wiring actually terminates in a 1/4" jack that plugs into the amp section so with a dual female 1/4" adapter I can use it as a cabinet with another head (which I did for a while because the amp section was hosed when I got it but has since been repaired) and/or I can run the amp section to another cabinet. It's not very big either so it doesn't clog up my tiny "studio" room.
 
It's a crazy old beast and I love it. It does however weigh a freaking ton but it's got wheels and I barely move it. Also there is no output trim which sucks because the line out is SUPER hot. I have to keep all the gain and volume knobs at 0 or it't too much signal so I can't get all the higher gain distorted sounds but the clean is soooo nice and all the EQ stuff still works so it's an awesome starter signal for pedals or sims.
 
Heh... sorry for the brag/rant about my old clunker but darn did I luck out with this thing. The Duoverb is really useful too but it is really ooooold sim tech so the sound isn't quite as good as I'd personally like. That model got quickly overtaken by Line 6's Spider line and I think pretty much everyone has moved on to their Pod stuff but I don't really know how those work. Are they pedals? Are they preamps? Are they DI boxes? All of the above? I really can't be bother because I'd rather buy a blues champ or one of those new little Yamaha modelling jobbies (I forget the name of them but they look like cool little units).
 
Cheers.

I like Redwirez and MixIR2 (the redwirez vst ir mixer). I can't seem to get anything I like from the Ownhammer Modern Mix pack. Everyone says it's the best, but I always end up using Redwirez. @Beepster...I'm using S-gear on my current project ( I used Amplitube on my last one) which has some Redwirez IRs. You can also download some free ones from their site, a 1960 Marshall I think.

I like the RedWirez, I also have Recabinet 3 (not 4) but they seem to be a lot more muffled sounding in general. I am by no means a great guitar player though, keyboards are my trade. The guitar is more of a side aid in the studio. I like good tone but I don't have the years of stage and rehearsal room experience on guitar that some on here can claim.

Anyway my main point was that there are a lot of good IRs available for a fraction of the cost of a complete sim, sometimes even free indeed. I think many of them (RedWirez too) you can also buy individually. And yeah, S-Gear uses some. So do a few other sims IIRC.

Just trying out some of the TH2 cabs on my bass buss and fiddling with the mic settings. I recorded this track using cleanish but slightly gritty dual output from the Line6 (got a pretty decent Geddy type tone). The cab, mic and room settings seem like they are going to help with this as well. Man I'm so glad I dropped the extra coin to upgrade.
 
I'm going to try some Write automation for wah/phase type stuff via my padKontrol (which has two nice fat MIDI pots) and the assignable knobs in TH2.
 
Also if you guys with the full version are poking around there's a funny little preset called Rumble Bee. It's not particularly useful for general stuff but it's fun to goof around with. It's got this really low, buzzing harmonizer thing going on that cracks me up. lol