On the Spark Mini, there is DSP applied to the aux in that creates almost a 1 sec delay between the input and output. I don’t remember the spark 40 having this problem, but it’s been a while since I had one. I know that PG boasts about the Spark 2 having ‘Sonic IQ Computational Audio’, which I’m assuming is just fancy wording for DSP as well. If it reacts like the mini, then using it as a ""FRFR"" speaker for another modeler will be a no go.