You could have it modded, but make sure it is done right.
I had my SACD Shanling seriously modded awhile back and it was well worth the money (i.e. No wishes to further upgrade since then, even after hearing EMMlabs and others first hand).
That being said...I've never been comfortable with the overall build quality/reliability of the Shanling CDP. I've only had one issue, but it still makes me more nervous than any other piece in my system. Thus, it's up to you whether to invest more money in such a piece.
Unfortunately, there are only a few companies that offer true high-end from a CDP without mods. There are virtually none that offer an affordable option. IMHO, you are not likely to be satiated very long with a separate DAC that only offers modest improvements, if any.
I'm not answering your question per-se, but I may be solving your long-term problem. Either save up for serious mods to your CDP or invest in one of the state-of-art CDPs. In the long run, you will actually save more than trying to constantly make modest jumps.
If you just HAVE to add an external DAC right now, try to find one that uses Anagram Technologies. Most DACs that use it sound good.