Funny that Srajan Ebaen mentioned this in the review of the ST500:
"In my extensive amplifier comparisons the ST-500 was considerably warmer and denser than three different Mosfet amps from ModWright, FirstWatt and Nagra; two valve amps (one Yamamoto 300B SET, one Trafomatic EL84 push/pull); one Power Jfet (J2); and two other transistor amps (F5 and Burson PP 160)."
"In my extensive amplifier comparisons the ST-500 was considerably warmer and denser than three different Mosfet amps from ModWright, FirstWatt and Nagra; two valve amps (one Yamamoto 300B SET, one Trafomatic EL84 push/pull); one Power Jfet (J2); and two other transistor amps (F5 and Burson PP 160)."