AFAIK, power draw from optical drives is not exactly substantial. In my personal tests, CD/DVD drives were only asking between 10-15 watts, and the labeled amperage reflects this.
Data transfer must be shared between any piggybacked IDE drives. This is further limited by the DMA mode, which you would want to make sure is optimized in your OS, as it might not do it for you automatically. Some IDE controllers are also restricted in the sense they can only support "up to" a specific DMA mode. An older controller could very well be natively limited in that sense.
I currently have 2x 708A units on one port, as well as 2x PREMIUM units on another build, but I have never tried to use drives simultaneously. As you mention, the "pause" you are experiencing during spin-up & eject sounds like there is a data and/or power burst, and the request is not enough to share equally, so one drive must briefly recede. It could also be an ATAPI command interference, though I'd assume it could be a DMA bottleneck.
I don't have experience with the auto-loading "AL" units you are using, though. I can't imagine they operate much differently, even on the power draw. I would suggest to investigate the DMA, see what you find & can possibly optimize. If you want to rip simultaneously, I would suggest using an alternate pattern e.g. when A is immediately done ripping, begin ripping B. As B is ripping, A enters "cooldown", perhaps extending the life of your drives in the process (versus non-cooldown ripping).