PCIe is fully broken by design on H6 SoC. There were some community efforts (mainly by Icenowy) to wrote some hacks that "translate" the broken part into usable data but not sure how successful that was. In conclusion if you want to rely on PCIe avoid Allwinner H6.
Also I strongly recommend avoiding tvboxes. For once they are not officially supported (and most likely never will) and for the other these things are sold as cheap as possible and vendors tell you everything that is necessary (including lies like claiming H6 tvbox has 4G of memory which is technically impossible) to make you buy their crap. Also there is a chance that even tough buying the same product as somebody else that internal components change without telling you and breaking potential ways to install Armbian. Solving such issues is up to you. Check https://docs.armbian.com/User-Guide_FAQ/#i-have-a-tv-boxtablet-from-insert-random-vendor-can-i-use-armbian-on-it
I personally have a pihole running for years on an Orange Pi One. Yes, that low budged Allwinner H3 with 512M of memory. It is way enough for that purpose. Orange Pi Zero (the older one with H2+ SoC) could do the same with smaller package but no HDMI (who needs monitor anyways when you have SSH). Its onboard Wi-Fi is crap though so don't rely on it.
