Siegfried, the preamps just have unbalanced outs just as Mike said, and I did not add any balancing circuit of any kind - I just use the unbalanced outs. The pin connections are:
2 "low" input
3 ground
4 "high" input
11 ground
12 +18V
13 -18V
14 output
15 +48V
3nity, that power supply is SSLTech's. He hangs around here. I haven't studied the 48V circuit and don't really know anything about it. I only know it's some form of a Cockroft-Walton voltage multiplier, and that you can adjust the output voltage with R1 and R2. I just consulted the LM317 data. I even remember experimenting with some resistor values that gave me over 50 volts.
I've also had some PMs requesting I put up a pic of my unit. As is usually the case, I just barely got it working for a big session, so it's not very aesthetically pleasing yet (well it is to me). I didn't even have time to drill rackmount holes and put it in the rack. But it serves the purpose well!
Pic here:
http://www.glt1.com/gl/Misc/SonyMXPRackUnit.jpg
Oh yeah, and instead of soldering right to the pins on the pres and EQs, I made some little PCB cards (using Press-n-Peel) for each module, on which I mounted 15 pin female connectors that mate with the pres and EQs (they're both the same). Then I did all my wiring to these little cards and just plugged the modules into em'.
15 pin connectors: Digikey S7048-ND
Here's my little connector card for the pre (pin 1 of the 15 pin connector at top):
http://www.glt1.com/gl/Misc/SonyMXPPreConnCard.bmp
And the one for the EQ (pin 1 of the 15 pin connector at top):
http://www.glt1.com/gl/Misc/SonyMXPEQConnCard.bmp
You can see that there are two solder pads on each type of card for the power connections so I could run power from one card to the next.
If anyone uses these card PCB layouts, keep in mind that you will have to shrink or stretch them on your computer/printer so that the 15 pin connectors will fit.
Glenn