What are best speakers for VTL 125 amps and 90dB ?

Pick up a used pair of Klipsch KHorns; they are great 'rock 'n roll' speakers and work very well with the VTL 125's, especially in Triode mode...

Are Klipsch K horns good for Jazz too?

"If my amp is clipping, wouldn't the solution be a more powerful amp?"

The VTL 125 is rated at 130 watts in tetrode mode. To theoretically gain 6 dB more headroom, you'd need to go up to 780 watts. Your speakers couldn't handle that.

So let's take a look at possibly changing speakers. The Vandersteens are rated at 86 dB. In order to gain 6 dB more headroom, you'd need 92 dB efficient speakers, which are not hard to find. Going in that direction is a much more practical solution, imho.

Duke

Thanks Duke. Do you have a speaker recommendation?

I think Khorns are at their their best with smaller scale music like jazz ensembles, guitar performances (say like Neil Young at Massey hall). However, you need a good-sized room for a pair of KHorns and they must sit directly into the room corners, flush and firm against the wall.