You can use the 2100 for the STR-K670P receiver but you will need to change the command mode on the receiver to AV1 per the instructions in this thread [Link: remotecentral.com]

Without the original remote to learn from you will be limited to whatever commands are preloaded in the 2100, which isn't a whole lot.

You cannot use the 2100 for the DAV-FX500 because Sony did not put any Dream System codes in any remotes until they made the RM-VL600 and the RM-V310, which were supposed to work but never did.