The Desfire cards may not be the right approach to this if security is not required. Anti Collision is a requirement of the ISO 15693 protocol. This allows you to read many tags simultaneously. Reading 10 tags is no problem depending on your antenna size and range requirement. ISO 15693 operates at 13.56MHz and is better suited for general purpose applications where security is not required. The tags can be in a variety of form factors. How large of an area do you need to cover? How large can the tags be?
Description of Anti Collision Sequence in ISO 15693 (TI TRF7960)
http://focus.ti.com/lit/an/sloa138/sloa138.pdf
One thing to consider also is the seperation between tags. If tags are directly on top of each other, this can cause mutual detuning of the antennas. A couple mm seperation usually helps. Smaller tags seem to be less affected by mutual detuning.
DLP Design makes a nice ISO 15693 reader with a USB interface. They also have an 8 channel version that can multiplex 8 antennas.
Another approach would be the selective addressing feature of the TI low frequency RFID tags like MUSA and SAMPT. The MUSA can be selectively addressed and works quite well when a small tag size(12mm) is required.