The best bet is to use the Line Out as it's straight mono, but since guitar pedals expect a signal at instrument level (high-impedance too, but that's not an issue here), you'll need to feed it sounds at a lower volume level.
Try setting your volume level to about the 9 o'clock position, so that it's pointing directly left. That will get you in the ballpark of instrument level. If you send too loud a signal thru, a lot of pedals (even delays, etc) will get an overdriven sound coming out, and some pedals can even be damaged by the overload. There are some, like the EHX Cathedral, which are designed to handle line level, but they tend to be pricier.
For most pedals, you'll need to basically treat your 'brute like a guitar, keeping the volume down, then running the chain into a pre or, if you want to grit it up some more, putting it thru a guitar or keyboard amp and miking that.