I don't see why you would have a problem with monitoring, Unless something is different with the US 1800 from the US1641 the monitoring is very functional and logical. As the monkey said, you can't set up a custom mix for multi track, but one instrument is very easy.  
You use the blend knob to mix the input with the computers output.
I find the headphones are very loud too. So what do you mean by not working,?? you must be doing something wrong.

Thanks Guyz...

It just wasn't for me... I guess I'm spoiled as I've had this ability since the very beginning of the digital audio daze as I did in the analog days prior to that...

I know of other ways to create monitor mixes, but none of those variants is what I want to do... Instead I've exchanged it for a Presonus Audiobox 1818VSL which only has 8 analog inputs, but it allows for 18 and I do have another converter that puts out ADAT so I will have 14 balanced balanced inputs and 2 unbalanced analog inputs. tho not true zero latency monitoring, it does do near-zero (<sigh>) with a few monitor mix setups...

Everything's a tradeoff, eh? We'll see if I like this one any better... I found that this one does claim VISTA64 support tho it appears I no longer need it as I've got the MacPro (Dual-Quads) running Win7Pro now and Sonar seems to scream with it and gives me (unusable) 1ms latency with the realtek built in audio! (I'm waiting for the Presonus to arrive)...

I immediately saw how the 1800 was really most suited to non-monitored recording (such as live shows) and that there were hardware options I could contrive to work with it, but I think the 1818vsl will be more what I'm used to.

Thanks again...
Keni

Hi Kenni Sorry to wonder a bit from your subject but I thought I would mention something I am planning for a monitoring setup. I've also have been expanding my system over the years and my next major purchase is a decent headphone monitor system. I have been looking at the Behringer Powerplay units. This is a new modular system and has a 16 channel input module ($299) that allows you to plug in up to 6 personal monitors ($199 each). The personal monitors allow the musician to create and save a number of personal mixes within the personal mixer and recall them. That way, other than setting up sends for each monitor signal, you don't have to worry about futzing things for the musician. I have two older Presonus FP10 units and they have been flawless with Sonar when I use it (I moved over to Studio One last year after being frustrated with X1). I believe the 1818VSL has the same 8 line out setup as the FP10s - I plan to connect each of the FP10's line outs (16 total) to the 16 inputs of the Powerplay input module and start off with a few of the personal monitor units and expand as I need for additional musicians. The entry level price maybe beyond what you are looking at since you already purchased the 1818VSL, but after looking for a long time at systems like Aviom, this seems like a pretty reasonable alternative that does not break the bank and gets me pretty close to the kind of system I wanted. I know I used the word Behringer, but they have been getting pretty good reviews on these units. Welcome to Presonus - I'm sure you will enjoy the 1818VSL (if my FP10's ever crap out, I will probably join you with a set of them). Take care, gs