Hey bikerman, A lot depends on the rest of your gear. If you post all the components in your setup, your listening preferences, then perhaps we can help you out. Not knowing the details makes it hard to offer suggestions.
I tried my ML Vistas driven by a pair of UPA-1s with a ModWright SWL9.0SE tube preamp and it sounded great. It gave a sweet sound but clear and open top end, very wide and deep sound stage. Imaging is also precise and bass control is very good.
Before that, I tried to pair the UPA-1s with two different ss preamps, primare pre30 and W4S STP-SE and they didn't match well with these amps. They sounded bright and a bit edgy. So the MW SWL9.0SE matched perfectly with the UPA-1. I liked the combo so much that I just upgraded my preamp to ModWright LS100.
I figured I would post in this thread since I started it sooo long ago. After much research, reviewing, and scowering the many online forums, I have finally pulled the trigger on a deHavilland Ultraverve 3 preamp to go along with my system. I get the feeling that I'm going to like the marriage between the UPA-1's and this new preamp, but only time will tell. Hopefully, it will be my last preamp...for a while anyway. ;D
Speakers: Two channel; Nola Viper IIa; Home Theater: Front - Def Tech PM700, center-Def Tech CLR 2500, rear- BPX Sub: Golden Ear Audio Forcefield 5 Amps and Pres: de Havilland Ultraverve 3 preamp, Integra DHC-40.1 pre-pro, McIntosh MC7150 Power Amp, Emotiva XPA-3, Emotiva UPA-1 x 2; Sources: Yamaha dvd c-750 disc changer, Panasonic BluRay Player; Musical Fidelity A5 cdp Display: 54 inch Panasonic plasma; Cables: Audio Art & River Cable IC's, Wireworld Aurora 7 & Shunyata Venom 3