In case anyone googling the topic wants to know how I sorted it out in the end:
Bought PIPO M7T tablet (t9 turned out to not have separate hdmi out),
upgraded it with stock rom to 4.4.2.
32 GB MicroSD.
Full HD, even with very high bitrate plays smoothly there.
Has usb otg, hdmi, aux and dc connectors.
Got headphones out connected to aux in my car,
HDMI out heads to hdmi->av converted and goes to car av inputs.
A USB 2.0 4x hub is connected to micro usb, to which I have connected dvb-t tuner, hdmi->av converter power cord and any pendrives I want.
Tablet is constantly connected to external power using DC in.
Works superb, couldn't been better.