The advantages of Audyssey can vary depending on the space acoustics and the quality of the receiver or processor. In my space, it is nice but not earth-shattering. In fact, the BDP-83's analog output (which doesn't benefit from Audyssey) is extremely well matched to digital output when connected to an Onkyo PR-SC885 (which does benefit from Audyssey). The 885 and is a more substantial processor than either the 970 or the SR5003.

If you upgrade the BDP-83 to the BDP-83SE, you are upgrading the power supply and the analog section. This upgrade will only yield a benefit to you if you are using the BDP-83's analog output, in which case you aren't using Audyssey anymore (no matter what processor you have). In that scenario, a product with a good, clean analog path is really all you need - and the Model 970 would likely be right up near the top of that list, especially considering your budget. The Model 990 has a few more bells and whistles, and it has better DAC's, but you aren't interested in its DAC's when the BDP-83SE is your source. A 970/83SE combo is actually a pretty compelling package.