Yes, the Zen F25 will be needed. It removes all factory EQ and time alignment and converts the 2 wire A2B signal into a flat 6 channels with 6 RCA or 2 channel Toslink (preferred). Yes, the Helix would be a great fit in the ST.
I have a 2025 job 1 ST which included the sun and sound 14 speaker B&O system standard. Front doors are 6x9 (up to 4" depth) and use F150 speaker rings, 2 1/2" mids that are about standard 3 1/2" size (about 88mm plus mount tabs - I did a 3d print to install 2" Kappa's). 1 1/2" Tweeters (housing size) are in the dash and snap in place. Left is easy access, right side you have to remove half the dash. Again, I used a 3D print to install Infinity Reference 1" tweeters that are smaller diameter than OEM.
Rear doors have 6 1/2" midbass and the same tweeters, but are wired as a full range single channel each side. I used a passive crossover in my install (OEM only uses a capacitor on the tweeter), but in the future I may add another channel and go active rear. In spite of the factory stated size, even the rear surrounds look like the same 2 1/2 mid/upper mid driver used in the doors. Also the same 2 1/2" size driver used in the dash. I took mine completely out. Sound stage is lower with the stock B&O amp, but I'm changing everything that will fix the sound stage.
The Infinity speakers were put in when there was no Zen solution out yet and do an excellent job of making it sound more like a premium sound system. Add a real subwoofer and it would exceed what most want. Now that there is a Zen solution (many installed and work fine as noted by cpassmore1, but mine has a quirk causing lots of issues (not NAV-TV's fault) . . maybe something Ford did in early Job 1's we don't know about yet? Once that is debugged, I have CDT drivers going in for the front stage.
Sound deadening is done everywhere but the first and second row floors, and the roof which is a task I always hate doing. Doors where easy taping the glass up and removing the inside plastic panel for access.
The only speakers that really need to be changed are the front stage and sub. With the DSP allowing multiple tunes, I will be using only the front stage and sub for my SQ driver only tune. Daily driver with passengers will be all speakers included.
