The old speedmax (rim) has a very similar geometery to the PR6 which is definitely lower than the speedmax disc. Canyon has increase the head tube by about 10mm (a bit variable between sizes) and gone with a higher bar that puts you up another 20mm so you are going to be starting 30mm or so higher on the new speedmax than you were on the PR6.
If you were running the PR6 without many raisers you will really struggle to replicate the position. Going to a different style clip on bar (something like what is on the speedmax rim bikes) will get you down a bit but the PR6 came with a low rise front end and you have the 10mm difference in head tube to fight.
Ultimately the CF disc is an intentionally compromised bit of engineering by Canyon. They designed the frameset around the CFR front end which does allow you to get properly low and has a lot of adjustability. Then they found on a way to slap on a much cheaper front end which compromises the bike in order to make a bike that is inferior to the CFR but more affordable. At the end of the day if the front end on the CF models had been as good as the CFR front end the CFR would be a much less compelling offering.
When I compare the geometries of these two bikes, they aren’t that far off. Head tube length is identical. Stack is 1mm shorter on the CF-8. I’m not a geometry geek, and admit to only understand the basics, but on paper the difference isn’t huge. Color me perplexed…