Popping while swiching channels - active ABY switch

[Longer713]

Hello guys!

I came today to you with big need to solve a problem with popping circuit.

There is one polish website/shop which sales DIY PCBs. I dediced to mod "splitter" board to use together with ABY switch routing.
Of course "splitter" circuit wasn't designed for adding footswithes, but I figured out to put switches routing between 1st lug of one of TL072 and later route signal to each channels before C4 and C5 caps. All works as it should, but as you might expect there is this nasty popping while switching each channels. I contacted designer of this board with question how to fix this but I only got answer with something about "grounding resistors" while caps are disconnected.

Is there anyone who could explain me how to add these resistors? What value and how/where connect them to ground?

Thank you in advance,

Schematics:

A/B/Y switch:
http://www.efekty-diy.pl/pdf/aby%20switch.pdf

Splitter:
http://www.efekty-diy.pl/pdf/Signal%20splitter.pdf