I had many problems with Fiio BTR5 USB driver I prefer not buy anything that uses Fiio USB driver.
One question is: Are Zen DAC or XDuoo XD05 upgrades over Lotoo Paw S1? It offers 120 mW/channel (240m mW in total?).
Or maybe you can recommend some separate DAC and AMP for that price?
Even the XDuoo Basic offer 500mW/ch with the Plus providing 1W.