I've had two modded Oppo players, a 970 and a 981. The simplest area to do mods on those is on the power supply board, since the power supply board could be easily removed and the components are fairly easy to access. And, no surface mount technology. I hope that's the case with your 980.
The mods on my players were more extensive, in addition to the power supply upgrades. The 981 had several capacitors and the stereo-channels op amps upgraded. (Not sure of all the details, since I bought the unit already modded.) The 970 had almost every capacitor (a lot!) upgraded but no op amp upgrades. A friend of mine upgraded the 970. He said that the power supply upgrade was no big deal; but as far as upgrades on the main circuit board (which takes up most of the chassis)--well, I doubt that he'd be willing to do that again.
So yes, audio performance (specifically, from the analog outputs) did improve, but it never really impressed me as "audiophile." I doubt that it's on par with your modded Sony.
I sold the 981 (nice player, I just wasn't using it) and still have the 970, which I use for watching movies and for multi-channel listening. FWIW, I don't use a processor. I feed the analog outputs right to a multi-channel amp and a powered subwoofer, so I have sort of a minimalist HT system. I'm actually quite pleased with it. I just don't think of it as audiophile.
Back to my earlier point, a power supply upgrade might be the most cost effective upgrade, and may well improve both audio and video, including audio through the HDMI. And it's relatively simple to do. As for the rest, well if I were going for audiophile-caliber multichannel sound, I'd be looking at a different player.