Jonathan,
I also have my IVa's on points. In my case I uses BDR pucks and cones. Same result. In order to keep the tweeter at its original height I removed the Dunlavy base completely (do not do this with kids or pets) which might have clarified the sound stage and opened the presentation more than any change except cross over mod's. The cross over is without a question the biggest improvement. See my review of that project at http://forum.audiogon.com/cgi-bin/fr.pl?rspkr&1164387495
I also have my IVa's on points. In my case I uses BDR pucks and cones. Same result. In order to keep the tweeter at its original height I removed the Dunlavy base completely (do not do this with kids or pets) which might have clarified the sound stage and opened the presentation more than any change except cross over mod's. The cross over is without a question the biggest improvement. See my review of that project at http://forum.audiogon.com/cgi-bin/fr.pl?rspkr&1164387495