I gots a 321 and I like it. The 321 is also a preamp as well and I don’t think the Shiit DACs are. I normally front the 321 with a Rogue RP-1 but that is down while I embezzle money to shop for vintage tubes, so the pre in the 321 has come in handy (others will see this as a negative). I go balanced out when running the 321 pre but single ended when running the RP-1 as it does not have balanced. I went with the 321 because it was on sale for 50% off because the new Di322 had just come out and the Di322 supports DSD where the 321 does not. 321 is a ES9018S Sabre chip and a Cirrus Logic upsampling receiver. Another reason I got the 321 was the reviews it had "warm" characteristics and that was a goal and I think it delivers. There is a used 321 on Ebay now for $1K. The 321 foot print is significant so be aware of that and it’s built like a tank. My sources are W4S moded Sonos Connect, cheapo CDP and Airplay Optical for radio.I don’t use the USB input much. Here is a review from a few years back. http://www.absolutesounds.com/pdf/main/press/HFN_Wadia32_June2015.pdf
