This is such a simple thing that I am ashamed to ask it! I've got an entry-level Hifiberry (DAC+/Amp2, software 20200901) running on a Pi3, feeding into a Marantz system. My PC is running Ubuntu 18.04 LTS, and using local WiFi. The system is able to use radio stations just fine. Now two simple questions (blush, blush!): 1) how can I play my audio files in the PC (do I need an NAS server app?) and 2) how can I "get out" of Hifiberry and into my Pi3 in terminal mode so as to e.g. add stations to radio.json? On the Hifiberry General page I see my PC, but when I log into this, I just get a tiny "true" word in the top LH corner - and nothing else!