I'd say, it is always a good thing having another ripper installed. CDEX is a very good piece of software, and I am using it more than EAC. The latter is used with discs, that are in not so good condition.
But if you can install both drives, you could continue using your Plex for that job.
If the ripping speed with EAC is slow, this indicates, that the CD is read twice in order to get optimal quality. Using a drive that is capable to report C2 to EAC, then ripping speed will be higher, at the same quality level.