The subs you were considering weren't going to be powered by your receiver's amps; the avr would only provide a pre-out signal to the amp of the sub. You can either use a plate style amp like many subs are offered with, or a rack style amp. I use rack style Crown XLS1500s (current gen 2 of these are XLS 1502s) for mine, with external dsp but the Behriner iNuke DSP series of amp with on-board dsp is popular for diy subs (particularly ported builds). Somewhat depends on budget, tolerance of fan noise (XLS are very quiet, Behringers not so much, some mod them with different fans but that can be risky), ported/sealed, dsp/power needed. Are you looking also at the flatpack enclosures to assemble or would you cut your own mdf/plywood? I think for a good performing budget minded sub you should read thru
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