I've always had on 1&2 out on my Delta 44 straight to monitors then the 3&4 out to a mixer.
Record/overdub out from Sonar on 3&4 to mixer using headphones. with 0 latency.
 
So I upgraded my computer and I thought I would use my Tascam us 1800 now and I'm adding another set of monitors.  There are 6 out on the Tascam. One set is suppose to be used for monitor as they are used with the headphones in the front, (I guess) and that would seem to be for 0 latency reasons. But I have never used any outs for my needs in the past. I just used the headphone jack and a mixer.
The other 4 outs on the Tascam seem to be for like mixing on a board. I don't need that...
 
What I would like to do is have 2 L&R sets of outs to monitors and one set to mixer.
 
So the setup is like this:
Input (mics, guitar, synth, etc.) to mixer then out mixer to the US 1800 out to computer. One set of outs from Tascam go to the mixer.
 
My question is, would it matter what set of outs go where for zero latency monitoring on my mixer as I record and overdub? 
 
Thanks!

I have the us1641 which is more or less identical. 
The 3/4 outs are the same as using the 1/2 outs. And the SPDIF is also the same. 
The Monitor outputs everything including the inputs. So is like using the headphones. I think it's only differance is the front panel control which is very handy. So I have always used those connection for my monitors. 
Sonar will have the outputs shown in Console view as example and you can easily send your master to 1/2   3/4  or SPDIF  
 
But generally you'll still hear your inputs regardless if you use the 1/2 or the Monitor. But there's no volume control on the front<< I think thats right. 
I guess we need to read the Tascam manual for details. 
 
http://tascam.com/content/downloads/products/535/e_us-1800_om_va.pdf
 

Thank, but nothing in the manual was helpful and sitting and looking at the back of the Tascam for an hour didn't help much either... lol
Seems I can't really do what I want to do.
S-Plat only has the two sets of outs (1 & 2 and 3 & 4) showing and is not recognizing the L & R main outs. 
 
I can send 1 & 2 out and main L & R out to monitors then send 3 & 4 to mixer as a work around. But I have not tested it yet with recording. What would be best is if all 3 sets of outs where represented in S-Plat.
 
The mixer I'm using for this setup is a Mackie 1642 vlz pro so no digital input.
 
Thanks.

The 3/4 and the SPDIF share. You can only use one or the other. 
I'd have to fire mine up to test but I'm pretty sure 1/2 or 3/4 (SPDIF) do not include the input monitoring.  They are just the DAW output
edit:  that's confirmed in the manual. . 
But normally we don't use more than one set of monitors while tracking. Two sets might be used for mixing reference so you can certainly do that.
 
monitors #1 patched to Monitor out used for tracking and mixing
monitors #2 patched to 1/2 used as second reference for mixing
Mixing board patched to 3/4 ( or SPDIF) 
 
 When you use a mixer like I do you can have input monitoring by using the mixing boards cue system. 
Your input is into the mixer which can be sent to the headphones or ?? outs, and you hear the DAW via a spare input channel etc. I use my SOLO function, this eliminates turning up the channel strip so the DAW doesn't loop back into the overdub. Each board is of course different. 

Yea!, that's kind of what I meant but in a back butt ward kind of way. :) I'll give it a try, thanks!
 
Yea I like how you channel your mixer. I normally run inputs into the subs then out to interface,.
I then send the out 3 & 4 from the computer back into the mixer with all relevant input channels set to the main as well, then monitor with phones for overdub. There are so many ways to set this stuff up it's hard to decide what way is best.

Hay Cactus I appreciate the help, it's nice to have someone to bounce stuff off.
I think we where on the same page, The only thing different is that I put my main monitors on (1 & 2) and put the other set on (monitor out), 3 & 4 to the mixer. Now I can control 2nd set with front Tascam panel and both monitor sets come out in on 1 & 2 in S-Plat. 3 & 4 to Mixer as monitor playback and record input on phones. The reason I set it up this way is to have my main monitors default in windows. The only problem is I will have to use a power strip for each set to turn them off and on as needed.. well that what I do anyway...
 
Thanks!
 
Thanks!  

My second monitors are Mackie powered PA speakers. I make a lot of backing tracks so I need to proof them via the PA. I use the mixer  to control the level of those as well as a small Sony Sub.   
Actually since I bought the Joe Meek pre amp I only use the mixer for monitoring control. I find it's faster then fussing with Focusrite mix control. 
 
My us1641 is still in service for recording full bands with my Laptop. I'm so pleased they updated the drivers. I'll get another 5 -10 years out of that system. I might  pick up the new us 16x08 just to stay new. The us1641 has more than paid for it's self.