Marshall Origin 50C Combo

Stil testing the amp and was verry happy with it at low volume but now after testing it yesterday together with drums and must say I am not convinced with it by higher volumes. The sound is much different clangy sounding and not going away while tweaking the tilt/EQ/presence, the sound changes but the clangyness stays, wich I absolute do not like... and I do not like to compromise things.
Using an Ibanez TS9 and a second stage overdrive Boss SD1 to work with the valves but still i'm not pleased with the high volume sound compared to the low volume sound and it feels like it is the speaker that does not handle it the same like it should, so I tried a different speaker in an extention cabinet with it on the 16 Ohm output and that sounds much better. The speaker in the cab is a Celestion Heritage G12H-75 15 Ohm in a Palmer cabinet, I ordered specially to get that problem solved, but did not solve, only concluded that the Celestion Heritage G12H-75 15 Ohm is much superior to that stock speaker that you can not replace it in the combo definitive because that one should be also minimum a 50w 16 Ohm speaker and the G12H is just 25w.
Tried it with the stock 16 Ohm speaker on the 8 Ohm output together with the Palmer/celestion G12H 16 Ohm on the other 8 Ohm output and not good, the G12H sounds louder and combined not really a good combination.
This said al by loud volume. Little sad because I wanted it to be great as like it sounded/ felt at bedroom volume...