This information is also posted at Focusrite's website

As a result of several enquiries about digital compatibility between The Liquid Channel and consumer interfaces, we decided to clarify a few issues. The Liquid Channel has a professional (AES) digital I/O, so officially the two formats would not be expected to successfully connect. However, owing to the minor difference in the data streams of each, 4 bits at the start of a block corresponding to de-emphasis for professional and SCMS (copy protection) for consumer, the standard rules do not apply. The only other variance is the nature of the electrical interface, with differences in level and impedance.

To investigate further we linked together an Mbox, having a SPDIF I/O only, with The Liquid Channel, using standard XLR to RCA (phono) cables. We found that the Mbox could send a digital signal to The Liquid Channel, for synchronisation purposes, and the Mbox happily received The Liquid Channel’s digital data. Although this was a successful example, you can never entirely guarantee that a specific arrangement will work; someone else’s Mbox and Liquid Channel may not connect so successfully.

The only way to ensure absolute compatibility is to purchase a format converter, which can be picked up from various companies (such as Neutrik).