Hey dwell,
So you want simple, cheap and easy....??? Yea, been there, doin' that. aa
Since money is a little tight, you can use one plate amp to run both Alpha's. The cheap one's on PartsExpress are about $100, and would
MORE than suffice for medium listening levels. (Sidenote; I know a fella that had racked up quite a few complaints from his fellow apartment dwellers using
one 15" Augie and a 25watt Radio Shack amp.) So a single plate amp would more than suffice. The baffle size of 18 X 40 sounds pretty good. As far as where to crossover (XO), the plate amps have a convenient little knob that allows you to change your XO from 40Hz to ?? Somewhere close to 180Hz I can't recall, but probably higher than you'll ever need to go. Somewhere in the middle should be fine. You ears will tell you what's best.
Agreed about your comment regarding the SIs. aa
Hope that helps young grasshopper.

Bob