What is the best tube pre-amp for my system

Snooker14
This Ayon CD5 source you have has a 300ohm 6H30 tube output buffer, and it's stronger and has better drive than most tube preamps have, but still not as strong as most solid state output buffers (which I prefer), so keep your interconnects below 4 or so meters long.

What you'll get then by driving direct is a sound that is true to what the source is attempting to give you, and not be influenced by any additional tube or solid state preamp colourations/masking as well, with all their added needless electronics in the signal path, plus also another set of interconnects as well.

Cheers George

Snooker14 hi, Have you tried direct connection between your Ayon CD5 and Pass 350.8?

As the Ayon has output level control at it's lowest setting from 0-4V variable.

And your Pass amp is 50kohm input impedance and only needs 2v in to drive it to max output.

So as you can see you don't need more electronics and gain in the signal path.
As doing a direct connection from Ayon to the Pass is a perfect match, impedance, gain and drive, and will give you the most transparent sound you can get, also save you a stack of money not getting a preamp.

Unless you wish to add some colouration by using preamp, then you will have the added problem of way too much gain.

Cheers George