Hi,
I bought the 909 over the 99 for use with Sonus Faber speakers -- there are some significant differences. The 909, along with its increased power, control and headroom, has a more colourful and dynamic sound with a smoother top end. The 99 can seem more "sparkly" on first listen but lacks the control and tonal colour of the 99 -- in my system anyway. You'd have to try them both, and they share a family sound, but the 99 is an excellent amp; the 909 is a great one -- again, in my system. The 909 and 99 have widely reviewed and these may help you decide -- but I'd hear both. I live in the UK and don't have access to the Absolute Sound but apparently the 909 is one of their favourites.
good luck,