Work around/replace receiver with bad channel?

Not very deep knowledge here, so thanks for advice!

I have an Emotiva Fusion 8100 which I'm using with Magnepan MMGs and a Hsu STF-1 sub, for music and movies. I have played around with surround speakers but so far have just used it for stereo. Since I moved to a new apartment, the (front) *left channel has developed noticeable distortion* at normal volume and above. To my ear it's more pronounced in a sort of upper-mid frequency band, definitely more noticeable on some tracks than others (loud middle-register solo violin seems particularly affected). I believe I have eliminated the speaker, cable, and source as causes, leaving the Emotiva receiver.

The receiver has the ability to copy the front L/R output to the SBL/SBR channels for either bi-wiring or an additional speaker zone, so I tried using those channels as fronts, but it sounded even worse, with both distortion and crackling. Additionally, the room correction system seems broken, since it does play the calibration sounds through each channel but fails to detect the attached speakers (also tried with a replacement mic), so I've been using default flat settings in the new space. Basically I think the receiver has a bunch of problems.

I opened the receiver up and looked for any obvious shorts, blown components, corrosion, debris/gunk, etc., but that's sort of the limit of my abilities. Pretty sure it's out of warranty. Unfortunately I don't have another receiver handy to swap in as a test.

Two main questions:

1) Am I risking damage to the speaker(s) by continuing to use the system, with audible but tolerable distortion keeping the volume pretty low, until I can get a solution in place?

2) How likely is it my problem would be solved by using a power amp between the receiver's pre-outs and my MMGs? I.e., is it likely that the problem is being caused *after* the receiver's preprocessing, at the amp stage, so I can bypass it by using separate amps? That was my long-term plan anyway since the Fusion, though rated for 4-ohm speakers, is I believe rather underpowered for MMGs. But if it is likely to be the pre-processor that's screwed up, I don't necessarily want to spend a bunch on an amplifier and then immediately have to shop for a new receiver because the problem persists.

Any guidance appreciated. Thanks!