Ive had 3 x 800x600, 3x 1024x768 and 3x 1280x1024 with tripple head analogue and digital edition recently on a 3G with x1900. Limitation of digital edition is that it only seems to allow for 60Hz. Analogue edition gives option of 75Hz too.

I've also had the same results with DH2G at the same resolutions (2x)

In the past, ive managed to use both 2 & 3 together or both of same type. recently however, with x1900xt I only seem to be able to use 1 at a time. Might be my monitor setup or changes in the newer USB powered boxes. Didnt get a chance to test fully - 1 box worked fine in this instance

S