Most AV receivers dont have bass management when selecting the multichannel audio inputs ( that you would you use to listen to multichannel DVD-Audio). You'll want to confirm if yours does or not.
I was comparing the 1600 and the 91 side by side at home last weekend and here's a few of my observations. ( FYI , I have a Sony 57" XBR2, and I was running both players in progressive scan mode.)
Both players looked very comparable in terms of color balance and picture detail. However, the 91 was able to portray lighting highlights/reflections more realistically. ( It is subtle , but my wife also made the same observation , lol).
I only noticed the flicker on the 1600 on one disk, Toy story. I switched out of progessive mode and it was fine.
The 91 struggles with shot-on-film TV show discs, it combs often on edits. You can force it into video mode to get rid of that. The test discs I used weren't incredibly detailed so I didnt notice any loss of detail. When I looked closely at panning detailed backgrounds, there was a little bit of moire. The 1600 handled these discs well without user intervention.
On shot-on-video disks ( e.g. concerts) , the 1600 does reduce "jaggies" but it only came to my attention when I was looking specifically for it.
I listened to two DVD-Audio discs on the '91 and they sounded fine. ( I am a two channel audio snob but am not yet enamored with multichannel audio, mostly due to the mixing style, so take that with a grain of salt.)
The '91s "letterbox-zoom" was more pleasing to watch than having my set due the zoom.
All that said, of the two I would recommend the 1600 as it does more things well and gives up very little in picture quality relative to the '91. Depending on the set and its state of calibration, its likely that you wont see any difference in picture quality at all.