External Balance Control

Thank you. I completely understand the “right” approach to address this need but I would like to keep my current preamp/amp. I know some folks use an in-line tone control device, e.g., Schiit Loki, etc., to tweak the sound and was wondering if there’s a similar gadget out there to just control the balance. I suppose it’s not that difficult or expensive to build a dual volume control box using premium grade attenuators such as Alps, etc., and that might be an option to pursue if there’s nothing out there for this specific purpose.

I wonder how hard it would be for Audiocubics to modify their external remote volume control to handle L/R balance instead of Up/Down.
Might be worth checking in with them:
http://www.audiocubics.com/http://www.audiocubics.com/specs.html

SMD Dact type 21 Stepped attenuator 
Buy two, one for left and one for right channel between pre and amp.

Why not just buy one (if they are truly transparent)

Why not? You'll never know...