I have the Bolder digital enthusiast mod to my SB3, which primarily concentrates on power supply upgrades and reducing the signal path of the digital output. A new voltage regulator is installed and the the analog outs are removed altogether. I use the modified SB3 in conjunction with a BPT battery power supply and run the digital out into the DAC of my GNSC modded Opus 21. The combo is very good and I really couldn't be happier with the results. Even good quality mp3 streams sound excellent. The most obvious result of the mods and battery power supply is a lower noise floor and quieter background.
Of course, the other school of thought is reclocking the digital signal and I looked at this before modding the SB3. I decided against it because I believe that my DAC/Opus 21 offers sufficient jitter reduction. IMHO, the effects of jitter in modern digital devices are largely overrated. Jitter is inherent in every digital device, but the levels at which jitter actually becomes audible is a controversial subject in the audio community, so I suggest you do your research before diving in. On the other hand, I think its hard to go wrong in maximizing the power supply of most any audio device, so I went that route and am glad I did.
If I were to go the reclocking route, I would look at the Empirical Audio Pacecar and use it in conjunction with a DAC modified to accept an IS2 input from the Pacecar (a Benchmark dac, example). I would be skeptical of any reclocking device that simply feeds back into your DAC via SPDIF, since SPDIF is a known jitter producer and arguably would diminish the effects of the reclocker.