Chris,
I received the scan you sent me. Nice photo. This was taken after 1895 as he has the post-1896 pattern Waffenrock.
He is infantry, as he has the flat chinscales, foot-troops buckle, and bayonet with company knot.
He is a no-rank private in the Garde-Korps, as he has the Garde eagle Wappen and plume with double collar and cuff Litzen.
His shoulder straps are blank. No number or cypher.
He has Swedish cuffs which makes him one of the five Garde-Regt. zu Fuß regiments.
So. He cannot be 1st or 5th as they had white shoulder straps and the 5th had unique Litzen. Blue straps of the 4th would look ligh in colour.
So he was with 2. Garde-Regt. zu Fuß (Berlin) Garde-Korps (red strap) or 3. Garde-Regt. zu Fuß
(Berlin) Garde-Korps (yellow strap) Yellow looks dark on the orthochromatic film of the period. Pick one.