I said above there was a company that built a digital ballast- guessing square wave but I'm not sure- for the 860W CDM, but they went out of business fast. My guess is that the lamps couldn't handle the ballast's output and returns sank the company.
My guess is they made a bunch of junk ballast that couldn't hold a consistent wave a would trash bulbs. Much like low quality, high frequency, digital ballast-can't hold a consistent wave at high frequencies and shortens bulb life and diminishes spectrum.
That, or like Philips has said, it's tough to keep a stable arc at high wattage with this tech and digital ballasts won't cut it for CMH lamps this big.