There are a lot of tantalum caps in the audio path after the MPX IC's. Every series/coupling cap in the audio path is Tantalum (there are 5 per channel). Most shunt/parallel caps in the audio path are poly film, with a few electrolytics mixed in. Basically, it seems that all the small value caps are poly film, medium value caps are mostly tantalum, and the few larger caps are electrolytic. The only mylar film cap in the audio path is in the MPX filter. There's also one mylar film cap across two pins of the MPX IC, but I don't know what it's for.
There's also a handful of resistors in the audio path, and they're all garden variety gold banders (+/- 5%).
In short, while the audio board's circuit design is definitely audiophile grade, probably top notch for its time, the parts quality seems to be nothing special, at least by today's standards.
Dave