You are correct that receivers are the standard approach for mass market manufacturers. The rated power output is also sometimes a figure that is difficult to achieve outside of very specific test procedures (one channel driven, for example) and most receiver amps have a difficult time with low impedance loads.
For two-channel performance, the 990 will definitely pay greater dividends than the 970 (some of that extra cost is tied up in better DACs and some upsampling capability that does some very nice things for two channel listening). It also offers some nice convenience features (assignable component and DVI inputs, editable input labels) over the 970. The 990 is
big, though, so if you go that route you'll need to be ready for it. As for which amp, I can speak from experience that the 7500 is a mighty fine amp, but if you've already had good luck driving the 9i's with 120W you could very likely get away with a 7125 and have a couple extra channels.
For cables, you'll need some extra analog audio cables - unbalanced would be fine, although if you got a 990 and a 7500 you would have the option of using balanced. My two favored sources for cables are
Outlaw (PCA for analog audio) and
Blue Jeans Cable . There are some other good online sources as well, though.