Welp, I've got it open, finally.  The top shell was in a hell of a state.  It'll require serious retrobrighting at my earliest possible convenience because it's liable to crumble if anyone so much as sneezes at it.  In the end three of the "legs" holding the system shut are actually broken so it's only held together by the top left and two middle screws.

Internally it's dirty as all hell, but that's not really much of a surprise.  Fortunately the bottom shell seems to be quite robust, it's significantly less yellowed than the top (to a degree that makes me wonder if it's been swapped over at somepoint.

Going to need pliers to remove the broken posts from top shell so I can get the screws out and into the SPC and front panels.

edit: pliers located, the SHVC-Sound removed and most of the shielding unscrewed.  It doesn't look too bad internally aside from a lot of crud to clean out.  haven't removed the heatsink yet, but there's no evidence of cap leakage or anything, which seems promising.  There is kind of a weird orange sheen on the board in a couple of places, but I suspect that it may be old glue because it's near the two bus connectors and the RF unit.

The corrosion on top of the SHVC sound shielding and on the controller port pins seems like they could point to trouble area.

Time permitting, I'll order a PSU and AV cable, and get the parts cleaned up over the next day or so, and hopefully I can get some sort of idea what the fault(s) in the unit might actually be.