I've been considering picking up a 6-string. I've played an Ibanez SR406 and thought it was OK. I haven't got my hands on the (discontinued) SR506. It seems that the 506 is regarded as a higher quality bass over the 406 (it is 100 higher .) Can any of you Ibanez fans out there inform me (and anyone else that's interested) what the differences between these two models are? Thanks.