Been out of the car audio arena for some years now, no time... so feel like a newbie again!

I need a hi-level to line converter as my BMW radio has no line level out and I can't replace it as
its part of the NAV, anyone advise as to which is best price\performance? R/F???

It will be connected to an R/F EPX2 then to a Soundstream Ref 405.

Thanks in advance
-Steve