One off the wall option is the MediaBox MB200 from PixelMagic systems. It is discontinued now but the MB200 had an updated clock for a higher quality SPDIF output.
Before I go on I will say the user interface is not the best and it has some bugs on he DVD streaming side.
I have one and I will also admit I have an SB3 as well.
For ease of use and acceptable music quality I use the SB3.
For music quality I always use the MB200 it's performance is night and day over the SB3.
This may be a stop gap solution and you can pick them up for around 100 quid on ebay.