Honestly I think losing the stacker for a stacker ipod mod is your only option then. Unless your navi has aux in for TV/Video? But also presuming you wouldn't be able to use the navi at the same time then.
The kenwood piece is nice if you have RDS. What model Lexus do you have? Models featuring a factory fiber optic antenna will not be compatable with any wired FM mod. I have had several ground noise problems with the HK unit myself, hopefully others were more successful. The best option is going to be a factory aux input adapter that uses the changer input on the back of the radio. If you have an IPOD, why would you need a changer?