Just got one of these off the 'bay. Price was right, and in both mechanically and cosmetically good condition, still has the protective wrapper on the faceplate. Went thru the normal checks before hooking it up to my speakers. DC offset is high, as in 48mV L, 75mV R. Well, that's not good. I've also reset the bias, it made the offset slightly worse. The amp has no adjustments for offset, so I went poking around the web, in AK, and on the 'bay again. Truth is, there isn't a whole lot of info on this amp. It probably isn't the best choice for high fidelity, it's more of a PA amp with RCA inputs and some exotic "Excelinear" circuitry, best left for a pro to fiddle with. But it's a monster, I've always wanted to own something like this, and this opportunity came along. Bad news is it sounds kinda rough around the edges, and I know it could be better once I get the offset somewhere more reasonable. This is where my quandary lies. Do I rebuild the current driver boards and hope I get it right (differential pair, I know) or do I go with the PC-1 boards offered by QUA-CO which have an offset adjustment built into them? Here's the real bad news, the PC-1 boards while fitting numerous Hafler amps were never designed for the XL-600, but can be "shoehorned" in. Either way is risky, what is the better choice? I'll throw some pics up next time I have the cover off.