I ditched my Waveterminal U24 and switched to the M-Audio Revolution 5.1 and don't miss anything so far. The M-Audio card has great D/A SNR (109db vs 110dB of the U24), but can go high on the sample rate (192kHz vs 48kHz of the U24). In fact I'm starting to like the M-Audio Rev 5.1 better than the U24 when in Foobar.
In your case, the M-Audio Rev 5.1 has SPDIF out too. It's not an external device as you required, but like I said, I like it more than the external U24. Check out its user manual at the M-Audio's website and see if it fits your needs. And, you can have it for less money as well (I paid $75 for it).
In your case, the M-Audio Rev 5.1 has SPDIF out too. It's not an external device as you required, but like I said, I like it more than the external U24. Check out its user manual at the M-Audio's website and see if it fits your needs. And, you can have it for less money as well (I paid $75 for it).