Did you duplicate the stock value of the output inductor, 11uH, and if it is larger what is the new filter pole. The original pole is 80kHz,12db/oct,
before the addition of staggered networks which appear to be Carvers work. Have you confirmed that the amp is not oscillating at RF frequencies
as this will also heat up the output inductors and mosfets. With the new output inductor in place is the amp still flat to 20kHz without loudspeaker load interaction that would alter high frequency response characteristics.
The pop at turn on is a result of the mute line not being properly toggled
[slow turn-on,quick turn-off]. The hiss is a mystery, my DIY Tripath based amp has no hiss problems, even with the 96db efficient speakers in my system. I don't think the hiss is intrinsic the the module. Good luck with your mod, getting rid of the extra parts in the amp looks like a real challenge. According to Tripath the toroidal shape of the original ferrite inductors was also chosen to suppress RF radiation as well as having low DCR,other inductor shapes are much worse radiators of RF. Some sort of shielding may be necessary around the new inductors.