Yep, the East pre-amp is much better than the Ibanez one in my 506. When time & funds allow, I'll get one in that as well. The mid-range sweep is very impressive.
The listing is wrong about which pre-amp it is, though, it is not the U Retro, but its replacement, the uni pre, so its even better than the ad suggested!
The Bass Direct listing still says the bass is on hold for some bloke called Dave