The tape output is a fixed line level signal making it unaffected by the volume control. Therefore it will not be useful in this configuration.
Biamping vs. Biwiring Pass Labs
Looking at the specs the X600 looks pretty much as powerful as a X350 but in mono. Would there be any advantage of using 2 X350s instead of 2 X600s and using one channel to drive the mid and highs, and the other to drive the bass (Nautilus 801s)? So you're using one per speaker but bi-amping...
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