Thieliste Hi.
Before you try/buy waist money/time on anything, try this.
Your only source the Ayon S5 has a volume control, and it already has a highly regarded (by tube lovers) a low output impedance tube output stage which is a 6H30.
This is just like having a unity gain tube preamp, but with the extra gain that you don't need.
Because your 6h30 tube in the Ayon S5 gives out 2v at 700ohms and your Karan power amp only needs 2v for full output before it clips.
And the impedance match ratio from the Ayon output (700ohm) to your Karan input (33kohm) is a healthy 1:47 ratio, you have a great match to drive direct from Ayon to Karan, no need for anymore unneeded electronics in the signal path.
Cheers George