OP,
well, I didn’t read your full post, so I missed ’no tubes in output stage’, I was ready to get my butt outta this chair, I just wanted to let you know how terrific the Cayin sounds in case you didn’t know. IMO it’s a terrific value and one of the best sounding amps I have heard, sure glad I tried it.
people give me contrarian advice, I do the same, so no offence, but with those efficient speakers, and modern integrated tube amps with easy and safe bias meters, I have to ask:
Is it possible you are limiting the ’sound’, what it’s all about, for practical considerations? Based on past experiences when you perhaps knew less, had too much power/heat .... IOW, things are different with your current setup.
Your speakers will easily fill the space with a 25 wpc amp, that ain’t too much heat, tubes or SS.
Tubes can last 10,000 hrs, for me that’s around 14 years. We can blow em, and we all want quad matched, but even so, it’s not a big deal.
Not having confidence about your tubes IS a big deal, pre or amp stage, which is why I always recommend you get a simple inexpensive tube tester. You test what you buy, check annually, check if problem suspected, most often get reassured it ain’t the tubes, ...
It’s not that your wrong, but you might not be right!