You are on a fun "stop over" on the never ending journey...
I look forward to reading your thoughts on how well what you are wanting to hear materializes. I've had my eye on the SEI-300 for years, just haven't had the resources when I've had the interest, or when I've had the resources, the interest hasn't been there.
I have a Cary SLI-50. This amp had a very short run back in the 90's that I have owned since new. Not much info out there on this. EL-34, push pull 30w/channel integrated. (Kind of what you would end up with if the Cary SEI-300 and CJ CAV45 hooked up...)
And to follow up on what has already been mentioned above, doing a cap upgrade will 100% take it to the next level! I did a complete recap of mine with higher end caps, and it transformed the amp. Granted, the amp is 30 years old, and the electrolytics needed to be looked after, and I could have replaced the film caps with the same Solen caps it came with, but I'm very happy I went the other direction.
This is a "forever" amp for me. All in one solution that just sounds "right" to me. Other amps have come and gone, and that will continue, but this is here to stay. Guess it's my reference. Hopefully you will find the same enjoyment with your CAV45.