I haven't had the chance to try an SM-400, as they're discontinued. The common word I've gathered about SWR is that the SM-400 was one of their better heads. The 800RB seems like a solid classic, and a much more viable option out of the GK line, as the rest only support biamping in 'biamping cabinets' which I undoubtably won't be pairing the head with. I'd like to hear some unbiased comments in comparing the 2. A highly probable setup for me will/could be 2 bag end 1x15"'s, possibly without the coax (possibly with, I need to retry the non-coax 1x15"'s). I was just trying an 800RB (for about the 15 thousandth time) and really enjoyed it, being played through the bag end, but am slightly turned off by GK's quality control, or there a lack of. From what I understand (correct me if I'm wrong) this stems from poor input jacks? If so, for the users of GK equipment, who've had to have work done, what was the extent of it? If there are problems, once cured, are they recurring? I'm very tempted to get the 800RB but I wouldn't mind a slight bit more warmth (I'm not fond of the SVT-ish tone) to my sound, which is what I hear the SM-400 has to offer. Thanks.