I have read many reviews of the Sony CX 355 Multidisc players 300 disc capabilities (or lack of )in shuffle/ random / store info etc etc.

- but no audio reviews by audiophiles with good sound systems - esp valve amps etc.

Any comments on the sonic ability, rather than the gadget trickery?

I use this with a TA DA90000ES digital amp and SSX90ED Speakers - through the optical output it sounds fresh and crystal clear.
Through the analogue output I thought that it sounded a little soft compared with my Sony CPD X3000ES (£450) but there wasn't much in it.
With valve amps try experimenting with interconnects to get the balance you prefer. I tried a silver cable but that tended to be too soft sounding so went back to copper. (I used to have an Audio Innovations S500 Valve which was a little bright so this Sony suited it well.)
In conclusion you will get a more muscular sound from a single disc separate but this player is perfectly respectable with hi res components.