Digby most of my statements come from Duffy.

Duffy gives details of the 3 'surviving' (post '57) ex Saxon Regts. For example:

IR NO 54 (Fusilier)
Designation Saxon regiment Sachsen-Gotha, 1756 Saldern, 1758 Plotho.
Uniform Blue coat, white cuffs, white waistcoat and breeches, fusilier cap.
Record Broken up after Seven Years War, and the troops sent to fill up IR no 33.

Duffy doesn't give specific sources for specific pieces of information, but mentions at the start of his Regimental Listings section:

For details of uniforms the reader is referred to C.Jany and A.Menzel, Die Armee Friedrichs des Grossen in ihrer Uniformierung, Berlin 1908 (Brititish Museum………) and the superb (and very expensive) work of F.G.Melzner and H.Bleckwenn, Die Uniformen der Infanterie 1753-1786, in the series Das altpreussische Heer (publication still in progress………..).

Very little indications seems to exist either way that I can find (despite much searching). However, in the STRICT spirit that in a near vacum the merest puff of wind must be utilised I offer the below as the merest ghost image of any sort of indication…...

On a dedicated SYW group it was stated to me that Englemann and Dorn not only elequently illustrate their uniforms, but explain that Frederick inherited his musketeer regiments from his father. All the 'new' regiments raised by Frederick were Fusiliers. Since the saxons were raised as prussian Battalions during Fredericks reign, they were surely NOT musketeer battalions.

Duffy himself seems to echo this, stating that Frederick inherited 3 Fusilier Regiments which he promptly converted to Musketeers, leaving all his 'old' regiments as musketeers, and that all the regiments raised by Frederick (the 'new' regiments) were Fusiliers. This would suggest the ex saxon regiments would be Fusiliers.

Not concrete, but I doubt I will get to see the above listed volumes so…….

You mention jany calls the saxons 'infanterieregimenter' (excuse spelling) and suggest this excludes them being fusilier - my understanding, at least for the SYW period, is that all the regiments were 'infantry regiments', some of which were musketeer, and some of which were fusilier, so jany listing them as Infantry regiments gives no indication in itself of their designation!?!?!?

All the best

Daryl.