I see no reason that the Marantz could not work well with the PS3IR-Pro. I would talk to your installer and ask him if he can program the Marantz 9500 to control a PlayStation 2. If he can do that, then he can use the PS3IR-Pro to control the PlayStation 3. The PS3IR-Pro is designed to respond to the PlayStation 2 infrared commands, and translate them into the corresponding PlayStation 3 bluetooth commands.
Most of the commands correspond directly with their PS2 counterpart. For example the Play command on the PS2 remote maps directly to the Play command for the PS3, the Stop command on the PS2 maps to the Stop command for PS3, etc. The only ones I know that do not map directly across are the color buttons for the PS3. I believe they are mapped as folows, but Mike or someone else would need to confirm this for you.
Playstation 2 Command -- PlayStation 3 Command
Shuffle -- Red
Program -- Green
Repeat -- Blue
Repeat A-B -- Yellow