I was one of the original doubters about the XLR, so I wanted to comment that it seems to work fine. I've now sent it to several mixing boards, and no sound men have said anything about it, so I guess it works fine out there. Probably not in the mix anyway.
I have also been in the studio lately, and at first I took in the 500 head and 112 cab; as usual, the engineer squawked about bleedthrough, so I unplugged the cab and made him take a direct feed from the 500 head's XLR. I know that heads aren't supposed be run without a load, but the heads seems fine after several sessions, and I had very specific reasons why I did this:
I HATE HATE HATE direct bass. It just has no soul, and to me sounds "rubbery." I know the 500 head's XLR out is supposed to have some degree of speaker emulation. I actually didn't hear any of that in the track, but I did retain some element of control and tone shaping. It worked great. The engineers seem to like it too. What they don't know is that the drummer and I were calling most of the session for more bass in the mix, so I just leaned over and tweaked the head - vol up a little, bass down a little, high down a little. Defined the bass better and brought the tone right into where I want it to be. I assume they were watching the meters, that's what they get paid for. anyway, let the engineer take credit, I got what i wanted without them futzing in ProTools for a long time.