I'm going to concur with HTADDICT here - even though you can use the multichannel analog outputs for everything, my standard advise for a universal player is to use the multichannel analog only for DVD-Audio and SACD, while letting a digital connection serve for regular DVD's and possibly CD's. It's true that the 990 can provide bass management, channel trim, and speaker delays for the multichannel analog input, but there's a lot more than that tucked into a processor's DSP section that no DVD player I've ever found can provide. Keep in mind that your player doesn't provide Dolby Digital EX, DTS ES, Pro Logic IIx, or NEO:6 processing - all of which either will or may be very heavily used when/if you set up for 7.1 (I say "may" because NEO:6 may not see as much use as the others, depending on personal preference). Any controls for Pro Logic II that it may offer are also going to be harder to access than with the 990.

Will the 990 be visible from your viewing position? If so, I wouldn't worry about controlling surround modes - the combination of the large display (which scrolls the name of the mode when you are making selections with the remote's DOLBY, DTS, and STEREO buttons) and surround mode memory will eliminate the need for an OSD. If not, you may find that it's still easier to use the 990 than the 59AVi simply because you have better control over the processing being applied.