Will there be a dramatic difference?

It is a decent step up but to make better there are 1 main fuse and 4 -2 per channel fuses on the power rails  that I would at least replace with Hifi tuning  fuses

Can you tell me what size fuses and where to get these?

How exactly do hi-fi tuning fuses make the sound better

I believe that is the name of the company.  The owners manual will give you the info you need.

I had a couple Carver amps back in the day.  Pretty good for 35 yrs ago and decent prices. The A 21+ is on the warm side sound wise like the Carver.

I have an A21+. What I really like about it is that if you hook up dual subwoofers to it, the gain adjustments allows you to tune it just like you like it. Reason is the lower you set the gain will diminish the mids and trebles much more than the lows. Hence it is an easy way to tune it to your ears. My best average adjustment, so it will sound best with all my different sources, Vinyl, CD, DVD, tuner and streamer is at 2pm, meaning basically two thirds gain. Enjoy, I do.