I would suggest that you save your money and consider a Pass Aleph series amp. If you need a lot of power, you
can wait for used Aleph 1.2's to come up for sale on Audiogon. These monoblocks are 200 watt/channel of pure class A, unlike the X600 which switches over to class AB after a few watts. This should be enough power for all but the most demanding applications. A fully class A amp
cannot easily be built to the wattages of the X600 (too
many problems with heat dissipation), but amps fully biased as Class A, such as the Alpeh, tend to sound like much bigger amps than their wattage ratings indicate. If you are interested in musicality, neutrality as well as a natural and detailed sound, you would be very hard-pressed to find nearly any solid state amps which will give you as much. They are not nearly as "pretty" as those X600s, they will get much hotter. but their sweetness,
musicality and lack of electronic signature is unsurpassed, even by the X600, which, although the electronic signature is slight, is still there. And they are cheaper. You'll just have to wait for a pair to come available on the used market.