Channel10, regarding you goal "1.", I both second David's recommendations, but be aware that, if what you are interested in is actually mostly the differences between the two synths outputs, and if you want to both ear and see where these differences sit in the frequency spectrum, there's also another way (which will work both for stereo or mono synth signals).
1/ Stack your two synth tracks into a track stack (or, if you do not want to stack them, route both of them to the same bus).
2/ On one (but only one of the two synth channels, insert a Gain plug-in as the very last position, leave gain at 0dB and balance at 0% and select the "phase invert" button(s) (both buttons if it's a stereo channel).
3/ Insert your Channel EQ analyzer on the summing track (or the bus Aux).
By inverting the phase of one of the two synths, summing them will only let differences come through. You can hear them, and the Analyzer will show what frequency range and amplitude they feature. No need for panning if you implement this approach. It is of course more appropriate if both synths signals have a lot of commonalities, and only fairly subtle differences, in which case it is more efficient to focus only on the differences, than to compare the two full signals. On the other hand, if both synths signals are very different, this approach won't be very informative because the difference between the two will be huge and all over the place.
Hi Arnoud, thank you for the suggestion, however even if signals are very close (two sawtooths from 2 different synths for example) it doesn't seem to work:
http://i66.tinypic.com/2l97hqh.png