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Pioneer M73/C73 vs M91/C91 opinions, differences, user manulas?

I'm not sure if this forum is a appropriate place to post such a topic but I cannot find any reasonable reviews or user manuals of mentioned above Pioneer combos. Recently I bought just by chance old Pioneer A757 amp and have fallen in love with it's sound so much that I decided to look for even something better from old Pioneer stuff. Have anybody had any experiences with mentioned Pioneer sets M73/C73 and M91/C91? I investigated that M73 is newer construction and you can switch between class A and B, but it is not Dual Mono but only two transformers. In contrast M91 seems to be true dual mono, but it is older construction and has no switching between class A and B, so I suppose this is class B only. Moreover I wonder if dedicated pre-amps C73 and C91 have 'direct' mode button to omit tone circuits and if they both have MC phono with selectable load impedance...? I will appreciate any opinions and suggestions... thank you!
Best regards,