When you talk about analog interconnects between preamp and amp, I take it that you are referring to unbalanced rather than balanced? The 990 and 970 share the same DSP chip (the very widely used Cirrus 49400), but otherwise there are a lot of differences - the platforms were developed completely independently of each others and are manufactured at different facilities. I haven't heard the two side-by-side in my system, but my understanding from others is that the 990 is a nice upgrade from the 970 for two-channel listening and a small step up for movies (surround sound). For analog sources, I don't know - the 970 does offer a switch to select from full bypass, 80Hz analog bass management, or digital bass management (with A/D/A conversion) for the 7.1 direct input, while the 990 applies digital bass management unless all speakers are set to large.