In my experience, it seems that the AV Famicom has cleaner audio and video output than NES Toaster, but...

It appears that the bass output of the NES Toaster is superior to the AV Famicom.

I was jamming to my MOON8 cart (Brad Smith's Pink Floyd DSOTM tribute) earlier on my NES, with output fed directly to my HiFi 2.0 stereo system with a very nice pair Polk Monitor 40s and a Sony Sub. I was listening to "Money" (my favorite track on the album) and was impressed by how good the bass sounded. Then I swapped the cart over to my AV Famicom using an adapter, and while the noise floor seemed lower and the output slightly louder than NES, the lowest bass notes produced by the triangle seemed a bit muted and it felt like I wasn't getting as much output from the subwoofer.

I have made several modifications to my NES including the PowerPak audio mod with a volume control pot, and a CopyNES USB dumper. Part of the shielding is also missing because I had to cut a big hole in it to fit the CopyNES so the slightly cleaner percieved A/V on the Famicom might be the result of added noise to the system due to my mods. The only modding I've done on the A/V Famicom was to add the D3/D4 inputs back into the P2 controller port for Zapper support. Either way the A/V Famicom definitely has cleaner audio and video, just lacking in the bass department.

I'm sure most TV sets in the 80s were incapable of producing sound down to 37Hz (the lowest bass note the NES triangle can accurately reproduce) but with a really good HiFi sound system there is an audible difference. Is there some way to mod the A/V famicom to get better bass out of it? The simplest solution that comes to mind would be finding the high pass filter and simply swapping a larger capacitor. Since the A/V Famicom was supposedly a cost-reduced model, I'd imagine Nintendo would try to use cheaper components, and a smaller filter cap may be a side effect of this cost reduction. Most HiFi stereo equipment passes down to 20 Hz or lower, well below the 37Hz minimum on the NES. If I could drop the cutoff frequency down to 20Hz or so would it make a huge difference? How low is too low? I want to be able to put the "punch" back in my speakers...