It all depends on how much you want to spend and if you have a DAC already. If you don't have a separate DAC the Audiophonics with the ES9023 is pretty good (I have one going spare if you want to PM me) and has stereo RCA outputs. I used the HiFiBerry Digi+ with my Caiman SEG DAC with an optical connection which was very good (I have one of those to!). More recently, I have been using the Allo DigiOne which does not have an optical connection (they claim the jitter is too high). Together with my Caiman SEG it sounds fantastic. You might want to try something from the Allo DAC range as well.
I hope that helps.
Cheers
Alastair
RPI4/PI2AES running PiCorePlayer/LMS-> AQ Carbon AES -> Topping D90 DAC-> Khozomo Passive Pre-Amp -> 4x Temple Audio Monoblocks powered by 2xLiFePO batteries->Van Damme Black Bi-Wired to B&W 804 Nautilus and Sommer Carbokab 225 Interconnects