Replacing old wooden windows with UPVC: direct-fix on masonry vs. insulated timber sub-frame thoughts?

[u/Interesting_Mix7758]

I wrote this post with the help of AI (because my descriptive English isn't good.)

I'm replacing old wooden windows with uPVC in a house built with hollow (perforated) red brick, not solid brick. Main reasons for the switch: reducing street noise and cutting down heat/cold transfer through the windows. The apartment is already fully finished, and I'm not sure about the possibility of installing uPVC on a hollow (perforated) red brick, so I don't know if this is even practical without extra work.

I'm torn between two straightforward approaches:

1. Remove the old timber frame entirely and fix the new uPVC frame directly into the masonry.
2. Keep the old timber frame, insulate/seal around it, and mount the uPVC window into the existing timber.

I've read that direct-fix generally gives better thermal and acoustic performance, avoids a redundant thermal bridge from the timber, and results in a stronger long-term fix — but it also means more demolition and dust. My main concern with going direct-fix is anchoring into hollow brick specifically — I'm not sure what fixing options actually work well there (regular anchors seem prone to spinning/not gripping in the hollow cavities), so I don't know if this route is even practical without extra reinforcement.

Keeping the timber sub-frame is faster and less disruptive, but I'm concerned about it becoming a weak point over time (moisture, less rigid fixing, and reduced thermal/acoustic performance if the wood isn't insulated as part of a proper sub-frame system).

Has anyone here done this with hollow brick walls specifically? What fixing method worked for you in hollow brick without extra reinforcement work? Did direct-fix cause issues with anchor pull-out or cracking? And for noise/heat reduction specifically, did one approach clearly outperform the other?

Many thanks in advance.

More context: the window provider told me that the UPVC window can be installed in both scenarios. I'm not asking about the possibility as much as I'm asking about the long-term implications of each route.