I buy 1 week ago the blackmagic multibridge bridge pro and im using the SDI monitoring provided by this hardware. Works 100% capturing and monitoring, my pc is very similar yours and workflow is realy good.
The only problem im having is the hdmi signal blink with bluescreens while capturing (I think is firmware faul during installation) but all connections works prefectly (components, composite, hdmi (out), and SDI). Finaly blackmagic mb pro is a realy good solution for capture and monitoring to leave the pc make his own work with and acceptable workflow.
I hope this helps you.
(Sry my english). >;)
CÁMERA: JVC GYHD251+BR-HD100
VTR: JVC BR-HD50
CAPTURE PLAYBACK: BLACKMAGIC MULTIBRIDGE PRO
COMPUTER: I7