I bought a PTAE8000U recently (I know, a few years too late but it works great!) and I have an HDMI running through the walls in my theatre room. The house was built in 2006 so I was confident that the HDMI would not be able to work with the 3d function. I bought a new cable and tried it out. I ran it along the crown moulding and did a good job of hiding it. I watched Avatar (obviously) and the 3d appeared bright and sharp. The only problem was that the video would cut out every 15 minutes or so. Through trial and error, I figured out that the new HDMI cable was bad (Murphy's law, I spent forever making sure I did a tidy job of running it back to the projector).

Anyways, to my surprise, I re-connected the old HDMI and tried watching a different movie (Beowulf 3D). The 3D worked! The only problem was that it appeared quite dim and I really had to play around with the settings to get it to brighten up.

My question is, would the HDMI have any effect on brightness? I will say that Beowulf is a bit darker and less colourful than Avatar. I haven't been able to watch Avatar 3D with the original HDMI because I gave the movie back to the owner. I can always get it back but I thought I'd check here first.

Sorry, I thought you were asking why a cable would make things dimmer.

In reality, a cable should not make any difference and you should not really need to change out your HDMI cables unless the old one is not working. Older HDMI cables did a good job supporting resolutions up to 1080p pretty well. Even some DVI cables could get the picture up to a projector properly. It's never a 'guarantee', but it is shocking how solid of a job those cables did.

Now, once you move to 4K video... It will change. True 4K video operates at twice the speed or more of most of the 1080p content that was on the market. It's tough to make that work across older cables, but still, you really have to try it before you will know for sure.

Good to hear you are having good luck with your previously installed HDMI cable. You should be good to go for a while to come.