Theta DS-pre

I purchased this unit new in 1988. I have never had an upgrade done. I have recently returned to music and am using the analog section to drive a Bryston 4bsst. My player is a Denon 2900.Speakers BW 804s.

Are the DACS still viable? Theta wants 8500 for an upgrade.

How would say an Arcam AVP700 Dacs compare?I have also considered Classe SSp-300, Linn Unidisk SC.

Very confused as to go with another external DAC or a high quality CD player (Arcam 33,36)

Gradually I am trying to incorporate a two channel system into a home theater. Dealer says ditch the Theta and go with one of the above units.
the preamp isn't very good the evs passive volume control is a nice improvement definitely