No!  There is no FBV jack on the XT Live!

A Popular Sub would be the Roland EV5

Below is from here:

http://www.mission-engineering.com/Mission-Engineering/Products.html

and here:

http://www.mission-engineering.com/Mission-Engineering/FAQ.html

"The EP-1 is an expression pedal only with a similar function to a traditional expression pedal. The EP-1 is a single channel expression pedal with no switch but features the same high quality sealed potentiometer and all metal construction of the other Mission Pedals. The EP-1 is also available with the R option mini toggle polarity reversal switch."

"Q: What type of potentiometer is used in the pedals?

A: The Mission Expression Pedals use a 20k Ohm custom taper potentiometer which works well with most of the devices we have tried so far. Expression pedal inputs typically look for somewhere in the range of 10k Ohm to 50k Ohm. The taper of the pot is similar to that found in analog wah pedals which is one of the reasons the Mission pedals are known to provide similar feel to a ‘real’ wah. This taper also works well for other effects, and for volume swells etc. The VM-1 volume pedal uses a 470k Ohm potentiometer. All potentiometers in Mission pedals are maintenance free, sealed units rated at 1,000,000 operations."

So I am questioning if the Mission Pedal as it is, will work with Line 6 Devices? Or does Mission do custom Mods?

The Line 6 Pedal as well as the EV5 has a10K ohm mono linear taper pot!

Below is from here: http://line6.com/community/docs/DOC-1472

Q: What are the specs for the Line 6 EX-1 Expression Pedal?

A: The Line6 expression pedal is a passive 10K ohm mono linear taper pot, using a standard 1/4 inch mono instrument cable.

This is the Schematic for the EV5 (I have it)

I haven't used the EX-1, is the fact that it's plastic really an issue?  Like does the plastic housing crumble when you use it?  Or is just the issue that it's plastic therefore it must be a toy?  Plastic is used in a lot different applications these days including products that need to stand up to a serious beating. I'm  thinking hockey helmets and things along those lines, I sure expect them not to shatter when I get hit with a slapshot, and I sure am glad I don't have to skate around with the wieght of metal. I'm a cop up here in Canada and we just switched over from the Beretta to the Glock for our firearm and a good portion of the gun is plastic, I expect it to work and perform without compromise.  There could be a very real beef with the EX-1, like I said I haven't used it and not all plastics are created equal.  If there are lots of reports of the pedal breaking under foot then I won't buy one but I won't shun it just because it's made of plastic.