OK, it's a slightly older version, the X1, but I've been busy over the last few years and never really got a chance to use the system. So, please excuse my ignorance on the subject.
Here's my setup.
PC connected to an Edirol UA-1000 via 2.0 USB. I want to expand the system to add more ch's by using either another UA-1000 or adding something like an ADA8000.
 
Here's my query on two scenarios.
If I record, say 8 ch's, and want to do a final mix ITB would/can I route those 8 ch's back in Sonar to ch's 10 & 11 so I can "mess" with the final mix and save it? Or would you go straight out of a DAC to a recorder?
 
Second scenario: If I want to mix OTB into an analog mixer could I do the same as above and send the final mix back into Sonar on two other ch's to save it and then go out to a DAC and to a recorder?
 
Thanks,
Brian
 

You might get more up to date advice in the SONAR X forum. This one is for <8.5.
AFAIK all your scenarios seem OK, but I'm really no OTB expert. Why not just try?

How many simultaneous audio inputs do you need to record? If it's less than the four you already have, there is no real reason to expand to a unit with more inputs.
 
As for you mixing scenarios, I think you may be over-thinking the process.
If you reduce your mix to two tracks(or one stereo track), there will be very little you can do to "mess" with the mix. You will have no control over individual panning, EQ, etc. of your various parts. The mix is essentially locked.
For maximum control, just work with the structure that X1 provides for you.
Route your track outputs to your Master bus.
Alternately, you can route the track outputs to other busses, that would, in turn, output to the master bus.
This way, you maintain control over the individual tracks, which is essential for dialing in you mix.
Effects that would affect the project on the whole would go in your master bus. This is where you might use a limiter like Boost11.
It's a good idea to "Save As" a new project as you go, so you have someplace to fall back to in case you mess it up(it happens).
When you mix is to your liking, you can Export, selecting the Master Bus as the source.
This will give you a recording of your final mix.
It's all built-in, very clean and simple.
Hope that makes sense.

The UA-1000 has 4 inputs on the front but 8 line inputs on the rear that I can feed from a mixer w/Direct outs.
I may want to record a few instruments live including drums so 8 ch's may not be enough.
 
I'll have to read up on Sonar X1 but I've read that it's sometimes difficult to get a good final mix because it's difficult to control multiple ch's at the same time ITB. Hence the question of using an outboard analog mixer and routing back to the DAW. 

Yeah, in that situation you would need the inputs.
 
"..it's sometimes difficult to get a good final mix because it's difficult to control multiple ch's at the same time ITB."
 
I'd have to dispute that assertion. While it's true that you may not be able to ride multiple faders at the same time, you have enough options available that this is not really a problem. In fact, unlike analog, you don't really have a total commit to your adjustments until you save them. Even then, you can still tweak stuff, and save it again.
Much easier than re-tracking the whole thing because that snare that's trapped in the sub-mix needs just a little more reverb.
Play with it for a while. Read up on grouping and buses in particular.
You can certainly route out to the analog mixer and back to the DAW, but I think you will like the flexibility and control that you have working itb.
You have plenty of options with the software and the hardware that you have. Ultimately, it will come down to which options work the best for your workflow. You may even find that a hybrid solution works best for you.
Explore, and don't be afraid to tank a project. It's gonna happen. Just be sure to "Save As". You can always go back and start over.
Good luck.

Number one reason to mix ITB= automation. 
Before using a DAW I used my Yamaha 01v and automated it with an Atari via MIDI.  
It's been 20 years since I had to mix manually and I would certainly never want to go back there. 
A well recorded song will almost mix itself anyway's. 

Yes,  I know I have a LOT of reading to do. I barely know the basics. I just didn't want to buy more equipment only to find out later on that I needed something else. I need to upgrade my mixer to a 16 ch with direct outs or get another 8ch. My present mixer is an old Tascam M208, in great shape, but it only has 4 busses and no direct outs so I'd have to use the "send" on the insert if I wanted 8 ch's out to the interface.
 
It seems to be a split topic when it comes to the Behringer ADA8000. Some like it(modded, which I could do) and others seem to hate anything "B". Anyone here have a Edirol UA-1000 they're linking with another interface?
 
Thanks for the input so far!

Don't mess with multiple interfaces if you can avoid it. For most folks, it's an unnecessary complication. You'd be better off buying a single interface with 16 inputs.
 
But the first question to answer is whether or not 12 channels is going to be adequate. IMO, 8 channels is more than enough to record a drum kit. Twelve channels would let you record a whole band live with few compromises. Plug 4 mics into the interface and 8 more into your existing mixer.
 
No need to route anything out and back in. You can do it all in the box without limitations. Mixing in a DAW is a joy. Nothing you do to a mix has to be permanent if you don't want it to be, so you can "mess" with the mix to your heart's content.
 
 

The UA-1000 has 8 inputs. If I'm reading the manual correctly you get 2 more by using it in ADAT mode. But, this is a bit confusing. If I'm using the UA-1000 with another UA-1000 or an ADA8000 it looks like I'd have more inputs but still only 10 outputs because the ADAT input goes to ch's 9 & 10. Also, it seems you can't use the 8 audio inputs at the same time as you would the ADAT inputs.
 
For those "in the know" does this sound correct? ?