Dominic
There's a few issues here.
1) Not sure if the native RSA external authenticator supports multiple instances - you've have to try it in ACS. Even then does the sd_conf config file tie you to a single RSA server?
2) Optionally if you have the RSA radius servers running you could create 2 external radius authenticators in ACS and do it that way.
3) You'd need to manually assign ACS users to one or other RSA instance. Because of how long an RSA authentication can take (possibly with multiple challenge/responses - think new pin) ACS would find it hard to do "unknown user authentication" if it had to back out of one authentication before trying another.
No to mention how long the client might wait for this to complete.
Its a suck and see situation. It might work, or it might not. Good luck!
