I tried both the A6 and new A4 Avant's, to replace my B8.5 Co Car, I came to the conclusion that both were too similar to what im replacing, A6 has better quality leather but the infotainment is fairly similar, and new A4, is a bit nicer than the outgoing model, but the old failings are still there, poor ride and so-so steering. The tech in the S-Line didnt seem all that much of a step up i felt.
But like yourself, I found the options list ridiculously expensive, I have B&O in mine and to have similar its a small fortune. same for the better NAV, i have MMI 3g in mine, and again on the new one, the equivalent is a pretty penny!