I'm looking to purchase a tripod setup. I'm looking at the Manfrotto line of products. Does anyone know if the video line of bases is compatible with photo line of heads? Specifically, the 546B base and the 400DXL head. I will probably buy a couple of bases but I would like cross-compatibility across everything I buy. I'm looking at the 546B because it suppose up to 44 lbs. I would look for info on the manfrotto website, but it appears to be down at the moment.
You are missing a part. The one that goes between the head and tripod. All you need is to by the one that makes the connection possible.
Most heads use either a 3/8" or 1/4" thread. You have to check with the 400DXL because I've never seen one. The 546B uses a 75mm fitting, so you need to find one of those with the thread for your head. If you buy multiple items, it is easiest to have everything with the same thread-size but, fear not, small adapters exist to make a 1/4" screw into a 3/8" one.