It's a single supply (27V/G) and split on the board by the TLE voltage divider.
RTFM, the instructions for what to do if you do not want bass boost are right on amb's website.
For your other 2 questions I have no idea what you're asking.
Am I the only one who thinks cheap and balanced just don't play well together? I mean if you're going to bother going balanced, which would presumably imply a balanced amp that cost roughly double what the SE version cost, why feed it crap?
I don't get too excited about the uncovered connections at the IEC, I've been known to do that from time to time as well. But my days of not connection safety ground are long over.
Get a refund now, not later, now. If you choose any other route you're nuts. I can't believe that power supply is mounted on what looks like a plastic sheet. epic
And holy shit, are those McCallisteresque drill chatter marks I see too?!?!? Christ.