If you are talking about the Bryston DAC you have listed it has outputs to an amp which should work fine for speakers which have their own amp. Plug the optical out from the 990 into the optical in on the Bryston and connect the signal cable from the Bryston to the input on the Dyns. That should allow you to play any source connected to the 990 through the DAC. If you connect the OPPO to the DAC you can bypass the 990 but you could be generating a ground loop right there.
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Music system
Model 990/7500/Magnepan 1.6 QRs/Technics SL1200 MK2/Aperion S-12 Subwoofer/OWA3/Sony NS75H DVD
APC H15 Power Conditioner

TV System
Large Advent Loudspeakers/ Polk center/Monoprice surrounds/Panasonic Viera 42 inch/Onkyo HT-RC260/Sony BDP S590/Directv


Home Theater System
Onkyo PR-SC886/Outlaw 7125 Klipsch RF-82 L/R,RC-62 center, RB-35 SR/SL, BENQ HT1075, Outlaw LFM1-EX/OPPO BDP-83/Directv
Harmony ONE
Blue Jeans and Monoprice interconnects
APC H15 Power Conditioner