whats the difference between guitar -> fx pedals -> amp input
and guitar -> amp -> amp fx send -> fx pedals -> amp fx return

also i have a gt10 multi pedal and a blackstar distortion pedal, i tried it like so
guitar -> distortion -> gt10 -> amp
hoping that the distortion pedal could be used as a boost pedal of sorts, making the input to the fx stronger when needed
however when i tried it out it didnt make a noticeable difference
as i understand it if i put the distortion pedal after the multi fx then it will distort the whole signal which could result in crappy sounds, id rather have the distortion first but i dont know if something in the gt-10 is compressing the input level or something
the effects loop is between your amp's preamp and your power amp. think of your preamp as a distortion pedal. if you're going to be using your amp's distortion, put everything in the effects loop that you would usually put after distortion.
The GT-10 has to run through the fx loop if you have a pre amp on your amp. You also have to go into the settings and change the parameters. This is explained in the manual. (You can download the manual from Boss if you don't have it). For a more direct explaination try this;

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