Mike
I saw your comments over on the PSA forum about this but that hasn't been my experience or that off most users. I haven't tried I2S as my Holo DAC's prefer USB and the Aqua prefers AES and in those scenarios the Red was easy to set up and sounds great. I've got a transformer modified Mk I but haven't tried the Red with it. Since the Mk 2's USB input is now reported to be the equal of the I2S input by owners and even Ted you might want to try the Red to the Mk 2 via USB. I also suspect that with I2S you are running into the pre-emphasis issue reported by several users that only happens with the two DS DACs. A couple of guys found that by changing to another brand of I2S cable the problem went away so it appears to be a combination of the DAC and particular cables that cause the issue. I compared the Red directly against the four times more expensive Aries G1 and while the G1 did win out in the end is was much closer than I would have thought possible. So see if you can borrow a good quality shorter USB cable and try the Red that way.
As to the manual agree it's not great but is pretty much the norm for those translated from Chinese. There are now as you said enough owners ought there, especially on Head-Fi, to help a new owner through any setup issues.
Jack,
The biggest problem I had with setting up the Red was following the manual instructions in the order given. Unfortunately, those instructions were to download the image file, format the TF card, then burn the image file to the TF card. When I did that the TF card bricked. It would have been very helpful if before saying anything about downloading an image file, the instructions said the included TF card already had the operating system on it so all you had to do was insert it into the unit. Then have all the information about downloading, formatting, and burning in a separate section on if you want to use a different OS than the one provided.
If the USB input of the MK2 is equal to the I2S input, it would seem going straight from the computer to the USB input would give better results as there would be one less piece of equipment, the streamer, in the chain. Then again, there is the argument that the computer is noisy and isolating it from the DAC by going over Ethernet would result in better sound but the MK2's USB input is galvanically isolated so that shouldn't be an issue and my server is running Fidelizer 8 pro in Purist mode configured as a network player. I need to try the Red to the USB input and compare that to the computer to the USB input though that will introduce an additional time delay between the comparisons since I will have to physically switch the USB cables. My head hurts

The best advice I have is to audition streamers and DACs, or streamer/DAC combos like the Lumin D2, that have a reasonable return policy. That way your ears will tell you what you like. Something else to think about is that components from the same manufacturer tend to work well together which is not always the case when combining products from different manufacturers.