I’d assume the XM antenna is non-directional because there’s so much less signal to capture for audio than audio and video. Also, we’d all look silly with little dishes on our car roofs constantly twirling around to face southeast.
I don’t know what they’re using (and I bet they don’t get specifics) but sound quality can vary quite a bit depending on atmospheric conditions.
I’d bet it would. I’m not using the tape converter and it sounds pretty good when other factors aren’t interfering. On average it sounds MUCH better than standard FM reception.