I dunno...with the Duatt and Quadratt in the tile row, that's not TOO bad. Maybe a second Duatt would make sense in the hole on the row...? As for the 4 hp hole in the middle 3U row, my suggestion there would be a Doepfer A-133-2 to give more CV control over polarization...being able to modulate between, say, an inverted and noninverted envelope would be pretty nifty, and a good fit in that spot. Also gives the modulation sources a little more to chew on...