I'm a big advocate of a properly integrated sub for mixing. It does help clear up the midrange by relieving the satellites from low frequencies it's not very good at, and you get to hear what really going on the bottom end.
My opinion would be not to choose the Samson stuff. You can do better...I tried the Resolv
120a yesterday (just out of curiosity), and it was faulty...60Hz hum with or without an input, and lifting the ground or swapping the polarity didn't help either.
Anyway, if you extend your budget a little, I'd suggest the
Blue Sky ProDesk system. Goes for just under a grand, and it's simply amazing sounding!
If you can't stretch the budget, then I'd suggest getting the
M-Audio BX5's, with the
M-Audio SP-8S Sub. That combo can be had for about the same price as the Samson combo.
I use
the BX5's as my secondary monitors, and think they are the best in their class...and I've compared a lot of small monitors...
Just my 2 cents...