Even though eganz was a bit terse with his answer, I think he was only trying to direct you to where the answers you seek might be available.
I have been following this forum for about 10 months and have never seen mention of modifications such as you inquired about in it.
Yes, of course you may ask questions. You are aware that there is a search function available to scan through old posts. Although not a great search function, and sometimes limited in availability (during peak activity), it can find possible answers to your needs. If used off hours, make sure you choose the "slowest search" to get best results.
Putting the terms "Panasonic RP-91" in as search criteria resulted in 129 messages. Although I did not read them, there might be someone who had modified their player. Most were in the "DVD Players" forum. It might be where your answers will be found.
There is lots of mods that can be done to dvd players.... I use a htpc and have an Immersive Holo3Dgraph2 card and have had a Panasonic RP82 SDI modded. Huge improvement in picture quality.
Ken Hotte has done some mods on dvd/SACD/DVD-A players.
Parts Connexion has extensive mods available for the Denon 2900. 4% Silver solder, Black Gate caps, damening of the cabinetry, higher quality resistors, better output amps, Vampire rca jacks are among the many mods done by them.
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