Yes. Even I expected people who own the GT5-A604 amp will come forward and share their experiences, but I think the no. is very few, atleast on tBHP.
Well as I earlier quoted, I am pretty happy with the performance of this amp, for the price I paid for it. I have not auditioned a 8401, so cannot comment on the comparison. If someone has auditioned these two amps on the same setup (same set of speakers and HU) please share your opinion.
As per me, the brightness factor is dependent more on the HU and the speakers. The amp itself might not make the sound signature bright and also, the brightness can be toned down by the right tuning. I have mated the amp with a Pio 5050 HU and GT5 series speakers, and the sound is anything but bright even at high volumes. Personally even I dont prefer a bright sounding system.