Thanks for the replies. Two guitars, two Stomps, two channels of one PA. Both HX Stomp patches set relatively clean sounding. The output of the PA is distorted as in sounding harsh/buzzy/unpleasant. Not distorted in a good way. Line level, direct from HX Stomp to PA channel has been tried. Converting HX Stomp line level output to balanced line input to PA channel has been tried. Neither has any positive effect. PA is not anywhere near its maximum output. Neither PA channel indicates an overload condition. Keeping input levels consistent, one guitar with HX Stomp, other guitar with mic'd amplifier into two channels of PA does not distort. Both guitars with mic'd amplifiers into two channels of PA does not distort. Two guitars, two HX Stomps, two channels of PA distorts. Does this rule out the PA? I don't know specifically how Helix works... Is it possible that Helix passes some digital oversampling frequency artifacts (normally inaudible) into its output and if these two Stomps are not synchronized in some way, then when combined in the PA, nasty sum and difference tones are created? The band travels and really wants a multiple HX Stomp solution to work, so again, any help greatly appreciated.