Hey Pat !
Good to read that you are enjoying the synth
I too have had (and still have sometime) hours of experimenting on it
What you are hearing is the filter being clipped due to the 3 oscillators being played at the same time. While this phenomena is usually useful for mono sounds; playing different chords will result in different "overdrive tones", which may sound weird if you are not aiming for this sound in particular.
To have a clean paraphonic sound with the triangles :
-Set the waveform knob levels on VCO 1 & 2 to the maximum (so that it matches VCO 3 which is always @ max level;
-Set the VCO 1 2 & 3 mixer level to about 60%
Now it should be clean ! The only side effect is that the overall preset volume will be quieter than mono patches that tend to have the waveforms cranked up in the mixer.
Hope it helps !