Actually, have a look at Recovery's Jupiter Spirits. This is a quad VCO module based around the CEM 3340 chip, designed to hit the general area of classic analog polysynth sound generation. The waveforms it outputs are triangle (great for the more organ-ish sounds) and saw (typical string synth waveform). Easy to use, relatively small, and doesn't cost a pile of $$$. You could follow this with something like Intellijel's Quad VCA, also, which would allow you not only to mix the VCOs down to a single signal, it would let you use modulation sources to vary the four VCO levels; if you use a quad LFO in conjunction with this, you could put all four VCO outputs in continuous asynchronious shift against each other...definitely an ambient sort of thing there.