Adx is tied to the account holder rather than a website. If you bought the site but not the company you might find that you still have no AdX account.

Have you tried the traffic through and NPM partner yet? Worth doing in advance - understand the likely gains before investing. AdX performance is more heavily influenced by the skills/dedication of the person managing it though, so mileage may vary.

Google is rather quick to recognise quality publishers. You don't need volumes of traffic, need to be a niche leader and above average earnings (may be significantly above average).

Also, absolutely no guarantee you'll earn more with AdX. There are a lot of brand related benefits (public rate cards / private deals etc). If you're not a seriously branded player your benefits may be overrated from the very start.

Bottom line ... if you want to improve revenues, sell the inventory yourself or look for boutique rep firms / SSPs.