I have seen many installations where the 165 drives a trackbar/GS on the HSI and a VOR RMI needle at the same time.
Yes, I have that and it works
The way avionics works is quite bizzare; must be a legacy of somebody wanting to sell more "boxes" decades ago... no reason why one cannot feed the current radial (in whatever form, quadrature, gray code, or whatever) into a CDI and have it determine the bar deflection (and the flags) purely from that input, and from what it's OBS is set to.
Come to think of it, if the CDI bar is done externally to the instrument, why are the flags done internally? The flags are also resolved purely from the received radial and the OBS setting, nothing else.
It may be simpler if the OP just wants a CDI for a VOR and isn't after a LOC-capable indicator. LOC/ILS would be something else, because on a LOC or ILS approach the bar deflection IS done by the NAV receiver; the OBS (contrary to what a lot of IR pilots have been taught) doesn't do anything.