Certainly you can series connect your cables without causing any harm, if that's what you're asking? Obviously it won't yield optimum sound quality, which apparently you already realize. With or without the adapters. And you can certainly use different combo's of cables throughout your rig (many of us do that).
Another option is to drive the extra cable pair on a tape monitor loop (if you have that). Use you tuner as a signal source when you're not listening to anything else; just turn down the volume control to zero when you don't want to hear.
Another option is to drive the extra cable pair on a tape monitor loop (if you have that). Use you tuner as a signal source when you're not listening to anything else; just turn down the volume control to zero when you don't want to hear.