I have a stock 10/22 synthetic. I put set-screws in the stock behind the trigger to lock the action in place, removed the barrel band and floated the barrel. But now the barrel points too low (compared to the sight line of the scope) . I have tried three different scopes and none can adjust enough to bring the poi up to the aim point.

If I understand the 10/22 correctly, the factory model locks the barrel to the stock and kind of lets the action just hang there. What I have done is lock the action to stock and kind of let the barrel just hang there.

Obviously, I can shim the scope to make it work, but my question is:
Do the aftermarket barrels mate properly to the action so the scope mount is parallel to the bore?

how high are your rings?
try using the burris signature zees with the offset inserts

Odd.  THere are plenty of people (including me) who have floated barrels without running into this.  Theoretically, the only thing "holding" the barrel up is the receiver where the barrel is clamped in.  I have even been told that removing the band and doing nothing else will inprove groups since the stock will no longer affect the barrel.  It is possible that your barrel to receiver fit is loose and causing the barrel to sag now that the stock is no longer holding it up.  

Check the tightness of the two hex screws holding the barrel block to the action.  If they are loose, that might casue the problem.  If they are tight, the barrel might not be fitting into the receiver tight enough.  

You could try getting an after-market target barrel.  If you do that, then you might as well install a competition trigger kit and get a new stock.  You aren't on a budget are you?

ETA:  Go to www.rimfirecentral.com  Those guys know as much abotu 10/22's as some people here know about AR's.