The Oade mic input upgrade is only good if you are to use the mic input. With the 48v option, you will not likely use the mic in on the d8. I would recommend the phantom power option over the d8 upgrade. It makes your mics sound better and gives added versatility on recording decks to be used for best results.
How best to answer the question depends on how you intend to give your mics 48v phantom, should you go that direction. With a 48v power supply only (denecke ps2, rolls 224, etc) you *may* use the mic input of the DAT deck, or you may use the line input. If you are getting the 48v phantom from a preamp (mp2, m148, sonosax, etc) you will *not* use the mic input, making the d8 upgrade worthless.
I would personally go with the rx version of the 853s, as it gives better sound than the sound pros version, and gives all around more versatility, IMO.
Good luck, hope this info helps.