If you don't need the extra power, don't expect too much, if any improvement, especially in the high frequency range. Around 1975, I bought one new. It lacked in the treble range. The output transformers was the problem according to others. The output transformers were said to have a slow transient response, and was said to make the highs sound limited, making it sound like it didn't go all the way to 20 kHz.
Tube amps use output transformers, and the better ones don't have this problem. In the past couple of years, a friend and I compared a couple of other early MAC amps, and still noticed the same problem, hooked up to totally different gear.
Other than age, and the possibility of some tired parts, the amp was musical, and enjoyable except for that high frequency problem. I think is was Accuphase that used this problem, for a selling advantage at the time. Onkyo and other receivers lack in the highs, output power is far less, that can cause problems, but they are still musical, at least some of the ones I've heard.
So, if you don't need the extra power, you might not find much that will impress you, by going to the MC-2300. A lot of receivers have a problem with 4 ohm speakers. The MAC won't, if it performs right. If it was better in the high frequency range, it may provide a better improvement, sonically.
There should be other newer amps out there that will give you more sonically. A lot of people say that Emotiva and Outlaw aren't quite up to what others can do in this price range. I use tube amps now, and haven't kept up with the latest solid state amps enough to recommend one.
The MAC amps were built like tanks, and it weighs over a hundred pounds. If you buy it, bring a friend to help move it. It was hard for one to move I remember, even though I was younger then. Even Rock bands and Discos used them because of their build quality, and reliably in its day.