I have experimented with bi amping for awhile now. For the low end I have used a plate amp, plus a crown XLS 1000 and XLS 1002.
In general, I like the class d in the crown amps to the plate amp. Tighter, cleaner bass.
I ran across a well reviewed little class D amp in youtube video showing it had respectable measurements. When looking for it on Amazon, I found they also had pretty much the same amp that could either be a full range monoblock or a sub amp. I figured for $50, why not give it a try.
I got it and right now I am running it with my subwoofer which covers from around 40hz on down. It produces a pretty tight bass sound. Better than my dayton 250W plate amp, which is not the best, but certainly costs more.
So if you are an audio cheapskate and/or wanted to experiment with bi-amping, this would be an inexpensive alternative.
When I first heard it, I thought of anyone looking to add a little low end to your Betsy setup.
https://www.amazon.com/gp/product/B07MXFDD2J/ref=ppx_yo_dt_b_asin_title_o02_s01?...They also make a 200watt version which given the inefficiency of my sub driver, might have been a little better match, but so far the 100 watt version is working well.