Chris, just to clarity, the FDE (Flight Dynamics Envelope) includes the aircraft.cfg and the .air file.

If the ADV installation includes it's own .air file, rather than aliasing the csx732.air file from the main CS_B737-200 folder, then the ADV aircraft.cfg probably says something other than

[fltsim.1]
title= . . .
sim=csx732
model=
panel=
sound=
texture=
. . .
. . .

If that's the case then it's only applying the modified aircraft.cfg values for drag and thrust without applying the modified csx732.air values, which will result in being very underpowered.

I don't have the ADV expansion, just the original 200, so I can't do any editing with the ADV.
How does the ADV perform without any mod?