Gerry,
As a fortunate owner of both an Ion and a Voyager, I can say that both boards are excellent at what they do. While the Ion can do convincing Minimoog imitations, IMHO (I'll leave the discussion on dead-on accuracy to others here), it also has filters modelled on the ARP, Boss TB-303, Roland Jupiter, Oberheim and others - 18 filter types in total. This gives the Ion fantastic sonic flexibility. Add to that two filters per voice (each being any of the 18 types in either serial or parallel), an arpeggiator, a vocoder, an effects section (no reverb, unfortunately, but chorus, phaser/flanger and distortion effects) and 512 locations for patch storage, and you've got a pretty capable polyphonic board. And you can route external signals into the Ion to boot!
No slight on the Voyager here, but the comparison really isn't a fair one. The Voyager is monophonic, where the Ion has 8 voices. The Voyager is true analog, where the Ion is virtual analog, albeit very good virtual analog. The Voyager is a seriously well-built machine using high-quality parts in an attractive real wood grain case designed for the ages (think 'Porsche' and $$$). The Ion is well-built and represents a good value, with the quality of the components on-par with the price (think 'Hyundai' and $).
That said, there have been some quality problems reported with the Ion. Although mine hasn't been a problem, others in the Yahoo Groups Ion forum have reported issues. It's hard to tell how many people have been affected. The last word from Alesis was that there was a bad batch of parts in earlier units. If you were to purchase an Ion, I'd suggest getting a new unit made recently (say April, 2004 or later), and steer clear of units on eBay. I bought my Ion in September, 2003 and haven't had any problems (knock wood).
Actually, you couldn't go wrong with either board. Or do what I did - get both!
Greg
PS - Putting the Voyager oscillators through the various Ion filters and effects creates some pretty wild sounds!
