I had a Pioneer LD player until a year ago, when I literally threw it in the dumpster. Although it had AC-3 RF digital output, the only way that I could have taken advantage of it was to purchase a RF demodulator that would cost more than a new Oppo DVD player. So all I was able (willing) to use was the analog outputs like you do. All my LaserDiscs sounded terrible in stereo, so I decided to make a clean break.
The short answer to your question is YES, your LD player should be able to benefit from the 990 either way.
If your player has AC-3 RF out, and you already have an RF demodulator. I would connect that to a COAX input on the 990 and you'll have a digital signal that can take full advantage of the 990.
Otherwise, you should be able to plug your LD player's analog connections to something like Aux IN. Off the top of my head, I believe only stereo modes and bypass will be available on stereo analog connections, and you will be able to apply bass management and speaker settings as explained in
this table. I believe gonk might have more info on his web site, unless he wants to chime in.