McIntosh MC 275 - what generation is better

Thanx a lot for such a detailed answer. Most of all i'm interested in Marc VI "improved bass" according to ads. Is it really improved? How?

"Bass improved and how"

Inside the MK VI, there have been many subtle changes in circuits and component values, while McIntosh also says that its much-vaunted output transformer-winding techniques have been further improved to give greater bandwidth. This in turn has allowed the negative feedback to be taken directly from the speaker winding, giving a higher damping factor and a claimed improvement in deep BASS definition.

Thanx again!

Hello Vad58, just curious if you ever got the mc 275 vi? I have never heard tubes in person but love what they got to offer sound wise except the heat of course. I have an opportunity to buy a pair of mc275 vi and run them in mono set up. I currently own Pass Labs 250.8  and I love the sound they create in my set up with  Martin Logans Summit X and I was told tubes will get me even better sound. 

If it were me I would make sure I audition the MC275s in my system before swapping out the Pass amplifier. You don't need as much power for the bass since its powered and the higher frequency is where the  MLs will need serious power.