if you're not volume matching with a DVM and test tone, all bets are off.
a dual-mono PS will give you best measured performance.
i had a hard time volume matching a balanced B22 with dual-mono PS and stepped attenuator between balanced and unbalanced - running unbalanced was wired dual-mono as well. i heard a difference, but i also hear a difference between the balanced outputs wired for unbalanced vs unbalanced outputs from my BM DAC1 - again volume matched with various amplifiers. the balanced XLR wired for unbalanced sounds better than the unbalanced RCAs. identical wire.
stick to the BOM. if you have a cap fetish, you could replace the ceramic compensation caps with some film or mica. space is tight though.
if you feel you need extra power, and/or you feel your source sounds better via balanced, balanced could be considered.
if you feel the need to go high-end with wire, i would recommend various Belden at $0.30-0.40/ft.
personally, i would splurge on a decent pot/SA. and if going with a single chassis, get an encapsulated/shielded custom wound TX.