Possible a Celestion Creamback would do it justice? Those are some interesting EQ settings!
Perhaps the Reaper is overwhelmed by low end due to it being 30w? I hope you have the
opportunity to give the Creamback a try.
I’d try putting the 12AX7 back into V1.
You could be onto something because hardly anyone has anything bad too say about the Reaper 55Hz speaker.
Some speakers just work better with some amps than others. A very good speaker may actually not sound as good with a particular amplifier than it does with other amps.

My POS 1997 Valvestate VS265 2X12 just kills it for live tone. Scratchy pots and buttons, but just nails the tone...so much low end you can feel air coming out of the cabinet but it never gets flubby no matter how hard you push it - and with a very mid-rangey bass, I need the bottom end on the guitar...
Years ago, a guy I played with had one of those. I do agree. It’s a nice amp. He actually loaned it to me for a set of events I was playing over a weekend. I found it pretty easy to dial in a good tone.
How many hours do you have on the DSL40c with your attenuator in use?
Attenuated tube amp usage speeds power tube failure.
Your description of tonal disenchantment reminds me of my Tiny Terror, when it benefited from a fresh set of power tubes.
How many hours do you have on the DSL40c with your attenuator in use?
Attenuated tube amp usage speeds power tube failure.
Your description of tonal disenchantment reminds me of my Tiny Terror, when it benefited from a fresh set of power tubes.
Maybe I should bias the amp. The local Marshall 'guru' (authorized tech Jack Spina) recommends 30 on the DSL40C.
I have lots of tubes that's for sure. Just trying to avoid making so many changes at once.