Ah, I understand. The decoder needs that 8V in order to "wake up" the electronics, after this it can then determine if it's running on DC or DCC and react accordingly. It's quite normal behaviour, not just for MTS but for any DCC decoder fitted loco. LGB advise not to consist MTS and DC locos due to this difference in running characteristics.
I think some folk mess around with the MTS CV settings to try and minimise the differences in running, but you'll never get it to be identical to a non-MTS loco.
The loco's DCC decoder is going to be either part of the main circuit board or may possibly be a separate decoder plugged into the main board. If it's a plug-in then it can be removed and some switches changed to make the loco analogue DC only. If the decoder is integrated onto the main board, you've got no choice but to remove the board and rewire - seems a bit of a shame to do that as it's an expensive bit of kit.
Here's a link to the service diagram of 23194.
http://www.champex-linden.de/lgb_pr...CEE8B6FB61485256EE000700BB2/$FILE/23194-1.pdf
Looks to me like the sound is also going to be controlled by the decoder on the main board, so you'd loose that too?
If it were me I'd say don't mess with the loco, just accept that has different characteristics and maybe try and run it only with other similarly MTS equiped locos?