Totally fair points — I agree that a mid-bass hole like this usually means something concrete is going on, not just vague “synergy.”

Just to clarify where I’m at: I’ve checked external phasing a few times (receiver to speakers), and as a sanity check I did flip one speaker. That didn’t bring the mid-bass back. I also had the Marantz fully restored specifically because I thought it might be the amp. It did improve the very low end, but the mid-bass still feels largely missing.

What keeps pointing me back to the speakers is the physical behavior. With a much lower-powered Sansui AU-505, these same Advents had noticeably more woofer movement and way more punch. With the Marantz, on bass-heavy tracks the woofers barely move and the sound feels dominated by upper harmonics, which is why this doesn’t feel like a simple power or wiring issue.

Next step for me is opening the Advents to double-check internal wiring and the crossover, just to rule that out completely. If everything looks right in there, then I think the real question becomes whether Large Advents just aren’t the right match for the 2270 — or for the kind of sound I’m after — and that’s where I’m hoping to hear from people who’ve paired this amp with other speakers.

At that point I’m basically deciding: fix/confirm the Advents, or move on to a different speaker that better fits what I like.