Billy, the main reason for toroidal core transformers in audio equipment is to minimize external interference (in the case of audio equipment we are referring to 60/50 Hz 'hum'). Well designed and manufactured transformers should never give an issue. But I guess you already know that smile

Regarding:
Quote:
"I am not sure how far a cap in a transistor circuit could drift from standard before there was a noticeable change in the sound quality on studio monitors."

In carefully designed and calibrated tuned circuits this is definitely an issue (low pass, high pass filters etc), however, my concern is that the caps are old and likely to fail, especially those in the P/S parts of the circuit. Old electrolytics are notorious for this.

BIAB & RB2025 Win.(Audiophile), Sonar Platinum, Cakewalk by Bandlab, Izotope Prod.Bundle, Roland RD-1000, Synthogy Ivory, Kontakt, Focusrite 18i20, KetronSD2, NS40M Monitors, Pioneer Active Monitors, AKG K271 Studio H'phones