I also just recently paired my ATH-50's with a Focusrite VRM Box. It's revolutionizing the mixing process for me and I think your headphone mixes will improve 500% by using one.
So I picked up the Focusrite VRM today for $79...and I must say it's a pretty impressive
little box.....quite a wide variety of monitors and 3 different "atmospheres"
to listen in...(VRM stands for Virtual Reference Monitors, in case you didn't know)
The Yamaha NS10, which they call the Japanese White Classic, a standard in most Studios...
KRK Rokit6 G2
Auratone 5C
An American Passive and British Studio, not sure what these are supposed to be...
Genelec 1031A
KRK VXT 8
Adams S2.5A
Rogers LS3-5A
Stirling LS3-5A
Some British Hi Fi speakers, both 80's and 90's, computer desktop speakers, micro bookshelf system, and 26" Flat Screen speakers.
It will definitely help with my mixes, that much is for sure...sound quality is quite simply "stunning"
It's like owning an assortment of high and low end monitors, having them hooked to your DAW, and being able to turn a switch to listen to your mix on each set...and compare how your mix sounds on each - that's a pretty good "reference" source if you ask me...dynamic range is 108db - that's pretty darn good too....
It connects via ASIO USB or S/PDIF (which is what I'm using, as the ASIO is limited to 48K, and I record in 96K)
Of course, as sharke says, it's not the same as actually listening to the REAL speakers, but it is a darn good substitute for spending about 5 grand on monitors to "compare" your mix in....especially when your working for peanuts in the first place...
Just thought I throw my 2 cents in...