I also heard that shrillness, but didn't comment on it, as I assumed the Gaveau was having a "winter voice" day when the inside humidity is quite low. As I recall your new hammers are five or six years old now. If they sound very good at installation, many rebuilders will only do a few touch-ups on the hammers, as they often prefer to let them wear in first. My Ronsen Wurzens are nearly four years old now, and I'm sensing that some voicing to darken the tone just a bit might be helpful.
Here is an easy ear test you can use. Next time your tech is there, at the conclusion of the tuning, ask that he use a small brass bristle brush to gently buff the metalic residue from the strings out of the hammer grooves. (It takes about three minutes, and it will probably be no charge or a very minor one.) With that done, listen to the piano. You'll likely find the tone slightly darker and more pleasant. But for people like us that give their pianos a workout, the brushed grooves effect will only last a few days at best.
(Hey, I said it was only a test!) If the shrillness returns, and if it's clearly not a case of moving your recording equipment farther back from the piano, then it might be time for some hammer voicing.