Does the Terratec-output (32bit) for 16/44 use the new or the old code and has this changed?
The old. But note your context in this quote. And see below.
For now I feel upsampling to 88 makes the balance shift to the high frequencies and makes instruments sound less natural.
*Here* you'd be using the new code.
And, after three days of consecutive playing I agree with you. For me it took albums like from Emma Chapplin to find out. Actually she should be the first for (me and) everyone to try out. In all cases so far, her voice (and that really is enough to judge) sounds annoying when things are not right.
Btw, the shift to the higher frequencies I can agree with for net effect. What IMO technically happens though, is that dynamics grow excessively high. Just watch closely what you (or your wife) can bear for volume, and note that this is not about "raw" etc. highs. This is something else which can't be measured ...