with the cork idea i was thinking of filling the gaps with reflectix then adding another layer of reflectix over the metal/reflectix alternating strips as an attempt to avoid impressions from the metal ridges. is there any reason you didn't do this? You seem to of gotten every spot imaginable with that reflectix! Great idea getting those door step spots also
but i do think after a little more research you probably had the right idea with rubber and not cork. I just found online "2mm rubber underlayment is equivalent in sound resistance to 6mm cork underlayment."
That leads me to another question - how thick is that base layer of rubber you got? I tried finding what you bought online at lowes' website but had no luck. Even went there to see if I could find anything close and had no luck, so it looks like ill have to source some online like you did.