Hello Dave,
Many thanks for being in touch.
Good question, for which there will no doubt be varying opinion.
It sounds like the previous owner liked his mods/drove this enthusiastically, and ultimately the decision whether to revert to ‘How Audi designed it’ or not, becomes a personal thing.
If it were mine, then originality would be king, and back in goes the original filter set up. If you prefer mods and enthusiastic driving then you could choose to leave it, and even consider adding other ‘upgrades’.
Not sure if this really helps Dave.
Kind regards,
Gareth.