Upgrade your ULN-2.
The 2d Card was introduced in 2008 as a massive hardware upgrade for ULN-2 interfaces (without the 2d card these are known as "Legacy" units). All ULN-2 interfaces manufactured since are known as "2d Expanded" units. The ULN-8 and LIO-8 were designed after the 2d card, and were built around it.
The 2d Card greatly enhances the DSP processing power of the ULN-2, adds a brand new ADAT implementation and also improves the clock of any unit into which it is installed. Of course, the ULN-8 and LIO-8 possess these features (while trading eight channels of AES I/O for the ADAT ports).
Upgrading to 2d
All ULN-2 interfaces that did not ship with a 2d card from the factory can be upgraded. You may choose to send your unit back to the factory to have the card installed or may do it your self.