#1
I want to record my guitar, but so far i've only seen the usb interface's that have a 1/8 output.

What I want to do is

(Amp)
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USb interface----Pedals----(Guitar)
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(Computer)

So that the usb interface can connect to my computer and that I can plug in my pedal signal and then have an (1/4) output that I can plug into my amp because thats how I want to review my sound not through headphones or a computer speaker.
#2
There's adapter head things that you can put on an 1/8 output that makes it a 1/4 output.
"I'm not concerned about all hell breaking loose, but that a PART of hell will break loose... it'll be much harder to detect." - George Carlin
#3
Alot of interfaces have outputs for minitors 1/4. If im reading correctly, can you just use that?

Even ifs its just an amp you want, pan to left and use left monitor output to amp. Then again I wasnt quite clear on what you intended.