I'm not using a 990, just a regular old preamp with three pairs of outputs. But I understand what you are saying.
If I did this I would run the balanced pre-outs to my amp and one pair of the single ended pre-outs to my sub using a Y connector on the pre-outs.
I can't see any reason why this wouldn't work but I wanted to get a second opinion before I start buying the components for this system.
The other option is to buy a preamp with a sub-out, but then I'm limited to only a few brands of preamps.


I appreciate the help on this, thanks...Steve