the other ingredients like citric acid and glycerine in the syrup will affect your pH for sure, but I'm not sure how thats gonna effect the flavor. The first rule when trying to change something on abeer (i.e. amount of hazelnut flavor) is to change only one thing, that way you can really notice the difference. that one thing should be the amount of extract IMO. Hazelnut syrup is extract made into syrup form, so your using the same thing but alot more sugar. stick with the extract i think.
Ditto on the white chocolate. Ditto on the chocolate malt. if you want chocoalte flavor throw a lb. of chocolate malt in and it'll get the job done.
drinking: mocha java porter, belgian pumpkin ale, Gary's oatmeal stout clone, AHS nut brown, catamount porter clone, double nut brown, rye pale ale, my oatmeal stout
conditioning: nut brown
next: saison, wit, american wheat, hefe, kolsch, blonde
gone: too damn many