"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