New speakers, new equipment, bi-amp, only 1 sub with Spendors, what a circle of confusion.
1. change only 1 thing at a time.
Listen to your most involving music on your existing system.
2. Change speakers only. More or less involving?
Speaker choice is done, keep the other pair in the garage for a few months while you mess about with various combinations of existing/new equipment. Settled, then compare the speakers again, ... more involving?
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now, move on to other changes, 1 at a time.
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I agree, a matching Pair of Subs would definitely be a step up
not just in amount of low end, but enhanced Stereo Bass. Every note has fundamentals, and they progressively become more directional than a bass fundamental: front firing, no ports, located near primary speakers as a Stereo Pair.
Bass Imaging: Where’s Wally? Where’s Ray Brown standing?