I think that the transport is really good. I compared it to recent Sony players and even to Technics A10 DVD Audio and Marantz wasalways better. I bought it in 1988, sold all the other, but still keep Marantz. I would be really glad to get a schematic and be able to mod it. I2S, no oversampling, might be interesting to hear results.
I bought the service manual since I have a player which has suffered an attempt at exactly such a mod, with terrible result (power supply, dac board and servo circuitry down). Apart from a dislike of non-oversampling stuff, I urge you only try it if you really know what you're doing. I'm servicing this player for a friend of mine, but apparent mindless poking around (don't know who did it, he bought it this way and within a week it died) has already cost me a week's work (non-billable hours ) so far. It looked ghastly inside. Nothing worse than seeing how a fine player has been modded to shreds.
The service manual set me back about $30. Since there are large pages in it (A1 size) it's nearly impossible to copy or scan, so you may want to get your own copy from your local service dealer. Otherwise we could work something out, but I don't have access to a A1 size scanner or printer which would make it impractical.