at low to moderate volumes, the stock xover takes away alot of the power available to the speaker. If you crank it up too much clipping or protection mode will happen. Just hook it up and find the best spot. The problem is not really watts it is current so even a higher rated watts amp can't supply the needed current. Amps that have worked well for higher volumes are Sunfire 300 or 600, carver mono blocks, high end carver tfm-75 or better. And I have always heard mixed reviews on the carver 500 series and tfm 45 and the 1.5. Unless the amp is designed as a mono-block it is usually best not to use it as one and if it doesn't have the high current we are right back at the beginning again. There are a lot of amps I have never tried and not listed that could work, and some of the ones I listed as marginal people use and say they are fine but it is best to bite the bullet and buy what will for sure drive the difficult load speakers. If you want tubes with ribbons the new Carver amps may work but I would bet it would have to be the higher series rather than the lowest one.