It’s time to check the digital clock – audio clock, that is. Any digital audio system with multiple audio sources needs to have a master clock, since even though two devices might both claim to be running at 44.1kHz, in real life, one might be 44.101 and the other might be 44.099 or, in the rare case when the clock rates match exactly, the leading edge of the clock signals is very unlikely to be at the exact same place. Designating one of the devices to be the master clock and telling the other device(s) to ignore their internal clocks and sync to the master clock will make for a much cleaner signal, and no clicks, pops, or static. Luckily, the Aggregrate Device Editor in OS X’s Audio MIDI Setup application allows you to set one of the devices as the master and the other to resample it’s audio at the master clock rate. Which device should be the master is not a hard and fast rule, so you may have to do a little experimentation to discover which works best (on some systems, making the TonePort device the master and resampling the built-in audio works best, on other systems, you need to do the opposite). For complete details on using the Aggregate Device Editor with TonePort, check the pdf document available on Line6's website.