Re whether balanced or unbalanced preamp-amp connections are better, I've tried both (but not, obviously, in an A/B comparison) and my take is that unbalanced connections are more convenient (cable thinner and more flexible), can be cheaper ma(but not necessarily), but are very slightly inferior in performance. This is with runs of 2 meters or less. The difference I've noticed, and described elsewhere, is (certainly) reduced hum on phono using a Grado pickup (known to hum with the AR turntable) and (possibly) even more transparent bass.
This is based only on experience with the 990, nOrh Le Amp II monoblock amps, and comparing Outlaw balanced 1.2 meter interconnects with the unbalanced interconnects I was using before, which were in about the $100-for-2-meter range.
Your experience may vary.