Lionel Alco D&RGW set

Not sure what this has to do with TMCC/Legacy, the QSI reverse unit is for conventional operation.  Since you don't specify an actual model number, it's hard to know exactly what you have.

A picture of the board would help.  I do believe there was a period in the 90s that Lionel used some of the QSI boards (DCRU).  Not sure if they used the sound system though.  Model # is needed in case there is some documentation on Lionel's website.

If it's the 18107 model from 1992, then that one did have QSI reversing unit boards, yet they still had the Lionel RailSounds 1 sound system.

6-18107  set and the reverse unit is in the a unit and is qsi as it says it on the unit and it is pre command, basically the same thing as the lionel reading T1 steam engine.  Sound is in the dummy a unit , you guys forget about lionels 1st digital sound over the terrible sound before that.  I believe the 1st digital sound was in the B6 semi scale switcher and it was great at that time.

No battery for that one.  G

Is it possible to add a battery so the sound does not drop out when you change direction for the reverse unit.

I don't think so.  I think that may be the very earliest RS.  Can you post a picture?

I did an upgrade to a RS 2.0 conventional engine though.  I was able to move the 2.0 chips into a RS 2.5 hardware board that used a battery and that worked fine, and allowed TMCC control of the Railsounds.  G