Well, I can't really give you any "peat-specific" guidance. But, I'm growing in coco, which is definitely soiless. As for coco, it's inert. B'Cuzz coco like mine, is also buffered. I need to read more on buffering, before I comment on it. BUT....I ph my nute mixes to 6.0 in my coco. The reason coco is ph'd lower than soil, is because it IS a hydro process. I water/feed everyday. I feed 400mL of water/nute mix per 1.5 gallon container.
Specifically, to try to answer your question, I believe the reason hydro and coco is ph'd lower is because the roots are getting "rinsed" with nutrient solution, instead of the nutrient solution creating a build-up in a soil mix, then sitting idle waiting for the roots to find them, if you will.

What I'd do if I were you and couldn't find any reliable info....start adjusting the ph in your nute solution to 6.5. Wait 3 days and read your plants for any leaf curling. If no curling is occurring, you found your ph--at least your really close to what they want. If you DO experience curling after the 3 day wait, start lowering the ph in your nute solution two tenths at a time. Adjust ph down....wait 3 days...read leaves. Adjust ph...wait 3 days...read leaves. It shouldn't be too hard to find what they like. I'd expect around 6.2 to be their preferred ph. But remember, I have NO experience with peat. So take my thoughts for what they're worth----hint: two cents.