[ChJL]

whereas the bottom end on the Erco really adds bass weight and impact.

hmm... having owned HypsOor and assuming that is superior to the Erco across the board I'm surprised about that. Don't know about SS vs SET bass characteristics though.
Even more so that since I switched from X26pro/HypsOor to AGD I never missed Ferrum set up.
Without a solid foundation (=bass), quality over quantity things don't stand strong imo.
That's my challenge "find tube amp on same, hopefully higher level" then current SS set up...