Which Streamer is a Major Upgrade over PS Audio Bridge II in a DSD DAC

All of them that play USB A.

Purposely got the DSD WITHOUT the card.

Don't know if you are running Roon or not, but can vouch for the Bricasti M5 Network Player which makes for an excellent Roon endpoint.

Maybe it would help if the OP, after apparently being quite satisfied with his current set up, is looking to change

Before getting a streamer I would consider auditioning an EtherRegen to feed the bridge 2. It really helped my system to sound better, and it will still be of value if you do get another streamer. PS is coming out with their own streamer with galvanic isolation at some point, which will feed the Dac via I2S. 

I am pretty happy with the Bridge II after converting my LAN to fiber last year.  I used to own a full Sonore opticalRendu (plus a uD and oM DX) setup with their best LPSs as well.  But that was when I had a copper LAN.  With fiber and utilizing a bunch (6 or 7?) of linear PSUs, my system has never sounded better.