McIntosh MC-240 sound quality question

I am considering purchasing a MC-240 from a friend who let me hook it up first. Currently I have an NAD M33, KEF LS-50 Metas and a KEF KC62 subwoofer. I used the preamp outputs of the M33 and ran it full range into the LS50s with out a sub. I never heard my system sound like this. It was easy to listen to and the low end really came to like and I did not miss the subwoofer as much as I thought. The amp is in original condition and showed no signs of distortion, but I know that it should be gone through, which is not inexpensive.

I understand that McIntosh produces amps, both solid state and tube, that incorporate autoformers. I am trying to figure out if what I am hearing is more a result of tubes, autoformers, or both. I love the convenience of solid state, but after hearing this sound, it would be tough to go back. Has anyone had experience with McIntosh tube amps, and solid state with autoformers, that could shed some light on the sound of each?

Thanks in advance.