Westcott Studio Strobelite Kit and Canon 6D help

+1 to Peter's comment about minimum M power settings.

I believe the 6D does not have a simple pc sync outlet - just as the 60D doesn't. Apollogies if I've got that wrong & disregard what follows . . .

You still have plenty of triggering options - some of them based on a hot-shoe to pc converter. If you go this route, you might as well retain pass-through to a fully functional hot-shoe on top. So consider the;

Pixel TF-321 Flash Hot Shoe Adapter

Unofficially there are two marks of this device - make certain you acquire the more recent incarnation.

With that, a pc cord link is possible.

Or an Ex Speedlite in the cam's hotshoe set to M low power (specifically with Canon Wireless Light/IR type disabled) would sync/trigger the built-in optical slave devices on your chosen Studio Strobes. It could be rendered completely non-contributing with an IR-only-pass filter over the flashtube/fresnel.

Or simple M only Radio triggers like the Commlite Comtrig T320 or higher, would get the job done too. Cheers