Try Vindigo
While AvantGo may not have an OSX conduit, Vindigo does.
And while you can't get your TV listings from Vindigo, it's a little known (but almost true) fact that the Vindigo and AvantGo conduits were both based on the same formerly-open "MAL" protocol. Over time, they have diverged quite a bit, but the last time I checked, you could still use the AvantGo conduit to sync Vindigo and vice-versa.
So, what you'd do is this: Install the free trial version of Vindigo, and get the OSX conduit installed. Go into the advanced preferences for the conduit and there's a place to put in a server name. Tell it about the AvantGo server. I think it's just at
www.avantgo.com. Sync and see if it works.
Your mileage may vary on this. As I said, the two implemetations are likely continuing to diverge with each release. While this still worked a few months ago, it may no longer work today.
It's pretty lame that AvantGo hasn't come out with a native conduit if that is in fact the case. I know exactly how much work it'd be to port it to OSX and it's not very much.