So then get the RK30. It's the TT30 with a urethane back. If Flux is able to sell you a pair of DS45 urethane backs, I'm almost positive they'll slip right into the Feedback base.
16 Gnu Swallow Tail Carver . 16 NS West . 15 NS Snowtrooper BIA
16 Burton Genesis X . 15 Now Drive
16 Flow Talon . 14 Flow Hylite