The larger LSi speakers present very difficult loads for an amplifier to drive - an amp like the 7700 is a good choice for keeping them properly fed. The 990 is an excellent processor, especially considering its price tag. Together, the two would be an excellent fit with the speakers you describe.

Whether to use balanced connections or not is not going to be dependent on the impedance of the speakers. The processor and amp both need to offer balanced connections (which the 990 and 7700 do), at which point all you need is cables . (The current stock appears to be a bit low, but Outlaw usually offers a range of lengths and packages of two or seven cables.) If you use balanced cables at all, I'd use them for all seven channels. When to use them is a source of much debate in this hobby. They were developed originally for counteracting interference over long cable runs in harsh environments (recording studios typically have a lot of opportunities for electromagnetic interference and a lot of need for very long cables). For short runs (a meter or so) in the much less EMI-noisy environment of a home the need for balanced is lessened, and some people prefer to avoid the additional circuitry required for a balanced connection when the run is short. Even over those short runs, though, some people have found that balanced connections help mitigate the effects of ground loops (which can crop up from time to time). If you plan to have your 990 and 7700 close together, you don't have to run balanced, but the 990/7700 will give you the option to do so if you wish to.