Both those links are from well respected sources when it comes to hifi-idiots. You know, the kind that buys 1.000 $ power cables, and hears a difference. Or that can tell the difference between an upsampled 192 KHz 24 bit file that has been created from an mp3, coming from different brands of harddisk.
Jitter does matter IF you have a recording setup with multiple sources because it will affect syncing the clocks from these different sources that will have a slightly different conversion latency.
Jitter does not matter much for audio playback on a consumer level (eg output only at 16 bits, 44.1 KHz), if it remains in reasonable limits. And frankly, there is equipment out there that has jitter problems, but it is extremely rare. If a consumer level device sounds bad, it's usually because of lacking filtering, not because of jitter.
HDMI will do very well for playback in a car. It just needs good input. Most mp3's downloaded from the net sound awful because the person who created them has NO knowledge and no speakers that enable him to hear the difference.
If you rip your CD's, experiment a bit and listen to them on good speakers. It won't take more than a day or so to find your own personal best settings.
The new, emerging HD-audio scene is one big fraud. Masters for 99% of the music out there are 44.1 KHz, 24 bit. There's no way they will be re-recorded at higher sample rates, as there is no need to. So if an audio engineer gets a request for higher sample rate masters, he will usually upsample what is available. The other respons to the question: "These don't exist", will not make the customer happy. And engineers usually are friendly people who will do their best to please the customer.
That doesn't mean studio's aren't slowly starting to use higher sample rates. Some even go up to 192 KHz, but that's mostly in film studio's that specialize in surround film productions. For audio, not many will go over 96 KHz, because there is very little use for these higher sample rates. The only use is a couple of rather exotic plugins that can really use them.