From what I have read about the rectifiers across the web and here at headfi, if memory serves me right, the rectifiers do matter; I would be always careful to match their electric characteristics properly to the amp in question.
I have no idea what tubes I got with my Quad, but at the moment I am floored with the sound quality.
On the matter of XLR, I have sold of (together with the solid state amp) the RCA-XLR cables, since they were (the XLR) the only inputs to that amp. Neither that amp was truly balanced (I presume), since the output was SE, and the innards probably confirm the similar to that regard as about the Quad.
Yet, I am using the USB A-B into the Quad of the MacBook Pro Retina, and of the Yamaha CDR-HD1500 will be soon using the coaxial out digital cable (hanging onto the ordinary RCA from that source, for few days more), so I am not sure if the need for the XLR will ever occur, it will be source depending.
Interesting you say "big time" in regard to the rectifier, it will be interesting to feel how it changes the sound (improves it). Feel free to describe, if you ever find the time.