I configured a similar setup - MX4000IT SW 3.1 (+BLb4 conected) <> BeoLink Converter SW1.3
<> BSd 4 (updated to current SW = capable of timer recording / 8GB Card) and tested this config
in both options:
V.Opt 2 & A.Opt 0 as well as V.Opt 1 & A.Opt 1
MX4000 and, just for testing, an other MX7000 both "understand" "A.Aux" as well as
"AV" + "A.Aux" (or "AV" + "Shift" + "Radio") and turn on.
Remembered, that a similar issue concerning "A.Aux" on BeoLink Aktive & Passive just recently
has been solved by a new SW 1.6 for these units ...
Double checked by changing the BeoLink converter to an other one (not older then 6 month)
- bad news - same result as before.
The problem seeems to be the BL Converter - obviously beeing not capable forwarding "A.Aux"
Called the B&O tech support and explained that issue. Tech support told me, that this additional
"A.Aux" isssue has not been known before and they will notify the SW guys in Struer ...