yeah, agree on the 5V rail. if you have an SSD in there, can you not ditch the 15k drives? save a bit of power/noise/heat?
I had an A4kT, and that mainboard has an "AT" type power connector.
I had a CSPPC060/CVPPC, 128meg, CV64/3D, Digital Boardcaster32, AD516, Ariadne NIC, Vlab Y/C
couple of scsi drives for audio streams
couple of UW scsi for video,
IDE4x adapter, IDE boot drive, IDE DVD, IDE Zip
Fans. so many fans.
it actually burnt out/melted the 5V "tongues" inside the AT power connector plug. i'd have to swap in a new PSU every year or so.
currently got a "Flex ATX" PSU in my A4k, but it's not running as much as you are - but they are smaller, quieter, and the amiga PSU's were pretty weedy to begin with.
its running an A3640, 16meg on mainboard, a "bigram 256", an xsurf100+rapid road, mediator A4000di, and an IDE2CF+4gig card atm, so nothing like your setup
https://www.overtek.co.uk/collections/flex-atx-1u-psu/products/seasonic-ss-350m1u-350w-80plus-gold-silent-flex-atx-1u-power-supply-psulooks like this has got 16amps on the 5volt line - 80watts? have a look at what the PSU you're running at the moment puts out. volts times amps = watts
12V line is still important, as is the -12Volts, otherwise the line-out level amps fed from the audio DAC's aren't happy. found this when putting a mini-itx PSU inside an A1200. another lesson in not corner cutting.
