It's the DAC in your Oppo that's holding things back, not the transport. I use my Oppo as a transport, sending the HDMI out signal to a much better DAC. It sounds like you've figured out that is the route to take.
With those beryllium tweeters, you might want to look at R2R or FPGA DACs. Sorry, I don't have a specific recommendation, my last DAC in that price range was the MHDT Labs Orchid, which is very good, but probably a little outdated compared to some of the newer offerings.