Hi,
Just my thoughts in addition to the other posts.
The Avant NG has an old version of Android, Yes needs a cold boot occasionally and has its quirks. It does work quite well, has 4K over all HDMI ports (we use), handles sound processing better and links with ML reasonably well.
The Avant MK1 has a modified Beosystem 4 inside which now has its hardware problems due to the 4K modification. As does the panel, both are expensive to fix. Shame that the beosystem 4 with 4K was not continued elsewhere in the product range.
My vote is the NG for the above reasons.
Beoaus.