The S.M.S.L D300 I reviewed was loaded with firmware 1.0. For a time, a short time, a firmware update to 1.1 was uploaded that enabled DoP (for DSD playback for those who do not have ASIO, such as on Macintosh.)
After a late night discussion with a fellow enthusiast, and many measurements, followed by more research, it looks like the S.M.S.L firmware update has been a real nightmare for some people, so bad I believe it has degraded the performance of this DAC overall. Some have even 'bricked' their D300.
Version 1.0? Yes, a GIANT KILLER DAC and a real gift to those who love native DSD conversion via analog filter. I stand by my review and findings. However, it sounds like newer firmware created a nightmare. That firmware was periodically available from the S.M.S.L website. Yes, it came and went, came back and left again. As of now, the firmware update is NOT available on the company website. It CAN be found if you look to the forums, but my advice? Stay away! If you have a version 1.0? Keep it and treasure it.
If you want to buy one? Make sure it comes with firmware 1.0! New ones did indeed ship with the updated firmware that, again, is no longer even available from the company. Bad, bad situation, and I am watching closely to see if customer service and engineering can work this out.
linked below are the user experiences. This is linked to the final page of thread, but if you want a fuller picture, go back about 10 pages and start there.