Converting to/from line level signal for guitar effects?
So I've got some effects pedals that don't get along with my Egnater Tweaker's effects loop, namely the HBE Frost Bite Flanger, but my Carbon Copy doesn't do too well either. I've determined the problem to be the effects loop (which is at line level), and the previously mentioned pedals won't accept line level signals without a significant volume drop and high-end attenuation.
So my idea is to convert the line level signal being sent from the effects loop to instrument level, run it though my pedals, and then back up to line level and to the loop's return. This would do the trick to get it down to the right level, but how do I get it back up to line level? It's passive so I wouldn't think you could go from -10db to +4db, right? I'm also concerned about introducing noise and tone sucking. Additionally, the send and return both have a different impedance, would I need to compensate for that?
Any ideas on a way to achieve this, or a better method that hasn't occurred to me? Any help is appreciated.