dore_m Its funny - its like you and I have the same goals, just coming at it from different directions.
Yes, and often quite different directions!
Regarding this one, do you plan to do any experimentation? The AmplifyDIY videos are very good (especially the follow up one) but he did not test the higher compression strength foams, nor the different thickness which according to the manufacturer of the exciter are very important for good results. He did not test size either, but that's less of an issue since we know how that goes: bigger is lower frequency (and moreover often one is limited in size to the available space, so it's a moot point).
Anyway, I intend to do some tests with various foams, purchasing from https://insulation.supply/custom-insulation-board/ rather than Home Depot (well, maybe I'll buy the first couple at HD, since it has 0.5" and 1" @ 15 psi of compression strength, aka 150 from the manufacturer). But from IS I could buy the following 2'x2' samples (which will ship UPS rather than freight), with the following price estimates (by me, not officially from them):
1000 @ 2" ($31 2'x2' boards in their boxes)
600 @ 2" & 1" ($14 + $7, based on 4'x8' cost ~ 1.8x the 150)
400 @ 2" & 1" ($14 + $7, based on 4'x8' cost ~ 1.7x the 150)
250 @ 2" & 1" ( $8 + $4, based on 4'x8' cost ~ the 150)
150 @ 2" & 1" ( $8 + $4, 2'x2' boards in their boxes)
For a very reasonable total of about $97 (HD sells only 150 @ 1" in 2'x2', everything else is in huge 4'x8' and each of those cost easily 40 bucks -- besides not having anything stronger than 250). In any case, better coordinating among us to avoid duplication of efforts and instead seek multiplication of results 😉