NAD isn't in my
processor chart at the moment. There are two offerings available at the moment - the M15 and the T163.
The M15 offers a feature set similar to the 990 (adds HDMI audio support but has lip sync delay with a max setting of 100ms rather than the 990's 200ms and lacks balanced outputs) but retails for about $3000 even before you add the matching M25 amp (another $3000).
Based on the $1000-$1100 cost difference you mentioned, I suspect you've been looking at the T163/T973 combo ($1500 retail for the T163 and $2000 for the T973). The T163 is an older design - not only are there the obvious differences (no DVI switching, no balanced outputs), but it lacks transcoding (s-video and composite video outputs are not available at the component monitor output), OSD data (including the setup menu) are not available at the component monitor output, there is a single global crossover point (although it is adjustable), and speaker distances are not individually adjustable (fronts share one distance, center is separate, side surrounds share one distance, and rear surrounds share one distance). Those are the items that caught my eye from glancing through the T163's manual. Feature differences aside, I can only speculate as to how the unit sounds in comparison to the 990, but I suspect the 990 would at very least hold its own.
I suspect the M15 could provide a bit better audio performance (it ought to at almost three times the price), but the 990's no slouch. I haven't seen any comparisons between the 990 and the T163 to know how they stack up, but if I had to guess (and I stress "guess" here) I would suspect that the 990 would have an edge over the T163, particularly in two-channel. Somebody else may have better first-hand information, though.