Chef- thanks for clearing that up for me, feel much better knowing it's safe to add an extension cab.
I was thinking off adding the 15" vintage mesa cab below the combo. Has anyone had any experience using an extension cab with the combo version of the M6?
I was thinking off adding the 15" vintage mesa cab below the combo. Has anyone had any experience using an extension cab with the combo version of the M6?

I played the Markbass set up and the initial impressions faded on me. And just by coincidence, the M6 I returned was being sold at $150 lower than the first time I bought it (it was used in the first place). I went back to GC last night and made the swap. So I'm back in the M6 camp.