I had a RSX-1056 receiver, and added a RMB-1075 amp. In my experience, and this is only my opionion based on that, it was not that big of a difference to the stand alone RSX-1056. Maybe a bit quieter/cleaner with a bit more low level detail. Volume wise, it is more power, but 125wpc isn't going to be a night and day difference to 75wpc internal to the 1057. You are nearly doubling the cost of the 1057 by adding the 1075, which for me didn't end up justifying the investment. I think you need to go up to the 200wpc RMB-1095 to really hear a significant difference. Now, when I eventually replaced the RSX-1056 with a standalone processor (RSP-1068), I did find that more of a jump in sound quality. My advice would be to save a little longer and get a used RMB-1095 here on Agon. As always, your mileage may vary.
Adding a Rotel RMB-1075
I have a Rotel RSX-1057 5.1 Surround Sound A-V Receiver used primarily for music and less for HT. I now have a Marantz SACD player and am absolutely loving this new format in multi-channel 5.1. Fabulous. Am building my collection of SACDs now. The RSX-1057 is conservatively rated at 75 watts/ch x 5 in to 8 ohms at 20hz-20khz all channels driven. My two main speakes are the B&W DM603-S3 with the full complement of B&W center channel, surrounds, and two powered sub-woofers. Sound is out of this world. I'm thinking of my next upgrade and am considering adding the Rotel RMB-1075 multi-channel 5.1 amp at 120 watts/ch in to 8 ohms all channels driven and use the RSX-1057 just as a surround sound processor. What would I get out of this addition? Would I get more out of my mains and center channel because they're now being driven by more raw power? Would I realize more of the potential out of my B&W speakers? WOuld I really hear a considerable difference going from 75 watts/ch to 120? More slam and punch, more detail, more information, greater soundstage? Thanks all.