Andy Evans wrote:

I am - there's a good sound in there somewhere, but I can't get rid of a really
steely treble. Tone is OK and detail is good.

The treble is 'steely' and yet the tone is good... OK.

Therefore I want to use a much better PSU.

Why? the rest of the CDROM wont have been designed with any care wrt
noise on the audio outs.

And also bolt the mech down onto a really chunky slab of alu. (like
the Flat Fish if you've seen one)

What makes you think that will make any difference?