Thanks for the comments, Charles.
The ART DI/O has been discontinued for some time. Quite a few of the parts I used in the mods are also no longer being made.
I phased out the mods to the ART DI/O when I first listened to an early, analog modded SqueezBox 2. To my ears, the modded SqueezeBox sounded far better than my full on Mensa level DI/O.
Whether this comparison travels through to the Oppo is for someone else to decide.