lewm - Oh, sorry. I misunderstood your question. I don't expect to record on both devices simultaneously, but I want to keep the option in case I decide I need a CD-R of whatever I am recording. Also, I do not yet know how the recording function on the Sugarcube will work when recording sources other than LPs. For example, I have numerous singles to digitize, as well as material on DVD, BD, and some soundtrack music I have on my DVR.
Good point about the impedance issues. I could use the Y cables instead to split the output of the SC-2 in order to feed the Marantz and my preamp's tape loop input. Perhaps that would prevent that potential impedance mismatch, and still offer the ability to record a CD-R. Although, would that have the potential to mess up the signal being fed to the Marantz and the preamp? Ugh.