OK. The results are in after a weekend of testing the little black magic squares..
I put them under the amp, cdp dac and speakers. All had bamboo butcher's block in place already. I placed these under the feet of the gear sitting on the blocks. It was going to be a challenge to say which thing led to any improvement as I did it all at once but here goes..
First thing I noticed was that the dac didn't like it. Lost a bit of focus. This may be because the dac is quite small and light or a different implementation may be required. So I removed them.
Next on to some CD sessions. (As background the Halcro was NOS and came without feet so I had it on some big sturdy round plastic bottle tops. This was, in retrospect, a prime candidate for some improvement. )
Wow! Where is that WEIGHT coming from? The orchestra is massive. Is it boom or bloom? Is it going to mess with the lower midrange? Answer was No. After extensive listening to several familiar classical works (piano concertos) I lost nothing but gained enormous weight and authority. Now for some Year of the Cat. Great album with plenty of nice analog instruments and very very familiar territory to these ears. Again, WOW! The bass notes (bass guitar or drums) are so tight you feel them. Yes not just hear but actually feel (I'm not talking massive drum solos just nice tuneful playing). Detail? You hear people say they heard things they never heard before? Well I've played this album hundreds and hundreds of times and yes, I heard new things. Like under a guitar solo there's another little thing going on. Notes I'd heard before but now I know what they're saying (micro dynamics, lower noise floor?). Instruments like acoustic guitar had more body and resonance. Background orchestral pieces had more cohesion and clarity in the mix. Just great. I recently tweaked the Halcro with an audio mat that took it to another level (well worth it even at $300). Now with the $4 black magic I got an almost equivalent improvement.
Back to the Dac for some DSD sessions. Again just awesome weight, scale, clarity and authority. Hard to say but I think the amplifier has a lot to do with this. Maybe the speakers too. But the cdp has definitely moved up another level with the blocks under it.
As the man used to say... "Do yourself a favour.."