OT-Need help w/doubleneck wiring

[Bobdog <bobdog@pseudobuddha.com>]

i have devised a doubleneck out of a kramer bass & a chiquita travel
guitar but i'm having a wiring problem:

each instrument sounds great when switched solo, but when i switch to
both (using a standard switchcraft les paul style relay switch) both
pickups lose a bit of amplitude. it's a subtle thing but enough to bug
me. by adjusting the vol pot (500k) of one down, the other will regain 
most of it's amplitude, but i want to use both necks at once w/o making
adjustments.  

each neck has one dimarzio pickup. i've tried a les paul style wiring,
i've tried a jazz bass style wiring, i've tried rick 4001 style wiring;
the problem remains to a different degree each way.

*switching phase didn't solve the problem*

i'm thinking it's some kinda load problem, so i'm gonna try some emg low
impedence active pickups today.

i'm also thinking about a 1:1 transformer combiner kinda thing. thoughts?

any other suggestions?

bobdog