I have an Ultrarendu, SMSL SU-9 DAC, and Arcam SA30 integrated feeding B&W 707 S3 bookshelves + RSL Speedwoofer 10s MKII. I was getting bothersome mismatch in timing between the woofer and the main speakers and was looking for a solution to add some delay to the woofer. I tried the MiniDSP 2x4 HD however I found the detail in the output to the main speaker to be lacking in whatever config I tried. I saw that the Wiim Ultra had dealy capability so I decided to give it a go. To make a long story short, what I ended up with was the ultrarendu → SMSL PO100 USB to Optical → Wiim ultra optical in → sub via sub out and to the SU-9 DAC via the USB out on the WIIM ultra, then analog from SU-9 to the SA30.
To my 54 year old ears this setup sounds as good as the ultrarendu going right to the DAC, and it let me add latency to the subwoofer. I felt there was a loss in clarity and detail if I used the Wiim as the endpoint or used the analog in of the Wiim.
So the takehome is that Wiim optical input seems to be pretty high quality, and the SMSL PO100 also appears to be a good device. The SMSL PO100 was a much clearer and detailed sounding USB → optical than the topping D10a which I also tried.
Hope that this helps someone - it took me a while to get to this point . . .
Dennis