Having used the NuForce Ref 9V2 SE for a year and a half as my reference amps and now having gone to the Cary CAD 120S tube amp, my feeling is that the VTL amps would be the better way to go. The NuForce amp tends toward brightness and with those Berylium tweeters, I don't think it would provide the best match (and I did hear that combination at a CES a while back).
That said, the NuForce amps use way less power and I've had much better customer support from NuForce than from VTL.
Another possibility would be to use the Wyred 4 Sound amps with a nice tube preamp. The Cullen-designed Wyred 4 Sound amps are reportedly great sounding amps that are perhaps a bit reticent in the extreme highs (probably what you'd want with the Ushers). Good Luck!
That said, the NuForce amps use way less power and I've had much better customer support from NuForce than from VTL.
Another possibility would be to use the Wyred 4 Sound amps with a nice tube preamp. The Cullen-designed Wyred 4 Sound amps are reportedly great sounding amps that are perhaps a bit reticent in the extreme highs (probably what you'd want with the Ushers). Good Luck!