Here’s a late opinion about how to make tdai-3400 sound its best.
I’ve had the tdai-3400 for half a year, and found it to be great. Without roomperfect it is so-so, but with it sounds wonderful. Thats not surprising and has been written several times.
I’ve primarily used it with a 400gb usb stick at the back (but also with direct ethernet streaming), both because it was cheap and because I thought the sound could not get better than this (no noise from upstream units etc.). But I was wrong.
To satisfy my curiosity whether there was something to gain I bought the Schiit Eitr USB-to-spdif converter. I believe it both galvanically isolates, buffers and reclocks the usb signal. I then play usb out from an odroid xu4 (with kodi currently) -> Eitr -> Lyngdorf coax in. After letting it play for a couple of days there is no doubt, the sound is in a higher class; everything is tightened up, clearer and smoother, better precision and more 3d, I can now sometimes hear sounds coming from strange places behind me which I could not before. The difference is quite obvious.
And the kicker is that the Eitr is only 100$ on sale from Schiit. I spent a lot of time googling before I bought it, and there are several competitors including a singxer and a mutec, but the Schiit seemed on level with the best and at the lowest price. The general opinion seems to me to be that streamers up to around the auralic g1 will benefit from the Eitr, meaning sms200, microrendu, the small Innous will benefit, and sms200 ultra, ultrarendu etc. likely also. But it is of course subjective and not every opinion read can be trusted.
I’ve read some debate whether the stuff upstream from the Eitr matters at all - Schiit says no, but some say they hear a difference with both source and usb cable. My odroid xu4 is not especially audiophile or anything, its maybe similar to the raspberry 4. I’ve bought a special usb cable so I can inject very clean 5v usb power to the eitr (it uses a little bit of power from the source, 100mA I think), but I can’t yet say it there is any benefit to it yet (don’t yet have a good 5v power supply) - but a few say it benefits. I am curious to test it with a better source, the Allo USbridge signature would be a cheapish option.
I don’t doubt those who say that an excellent dac (I believe I’ve read > 2000$) into the upgraded analog inputs on the tdai may be the very best, but the price is also in another league.
So, if anyone is using usb in to the tdai-3400/2170, or streaming directly to it, i’d say try the Eitr with any usb source, you may be surprised.
Note: the Eitr will be discontinued, thats why it is only 100$ now. Schiit supposedly have invented something thats a bit better, but they say they won’t put it in a separate unit like the Eitr, only build it into their own dacs. I have no relation to Schiit what so ever, and I don’t have any other Schiit gear, but I find the Eitr to be crazy value for the money.