Discovering my new IDA-8

, I am also facing new questions as I go...

Unless I have missed it in the manual and scanning through this very extensive thread, I didn't find the answers to the following ones:
-> What is the maximum section of speaker cables (diameter [mm] of area [mm²]) that can be used 'bare wire' (through the hole in the IDA8's terminals)?
I had borrowed some speaker cables (Van den Hul CS122, with a cross-section area of 2.96 mm² according to its specs) to test my new setup, but it seems the cable is too wide/thick to fit well 'bare wire' into the speaker terminals (through the holes transversal to the terminals). (I know I could use banana-plugs (or spades), but I would prefer not to, as I don't need to switch cables regularly, would prefer a solid connection, and this would save me some costs and also space in case of banana-plugs etc.)
-> Can the 'extension port', which is of physical USB-format, be used to power my Chromecast audio (which sends its signal back to the IDA-8 via the optical input)?
(That would save me space and power-socket space.) I don't know if there is any risk in doing so, e.g. if one would inadvertently select that extension port as input while the Chromecast is connected to it. I know Nuprime has other, more feature-rich streamers too, but for the moment I'm quite happy with the limited Chromecast functionality and already own one.