I typically duplicate the flow to make a playback version and change the dynamics as well as a ton of other tweaks. For me I find this generally less painful than tweaking MIDI data and more easily readable. YMMV.
Go through the Base Switches that your score is likely to use on the Piano stave, and change the Max Dynamic Range to something lower. For piano and percussion sounds, Velocity is usually king, but you can try the CC11 max as well.
You might also examine the “Playback Options Overrides” stuff. If you adjust things like the “Dynamic Power Curve” here, it will override whatever the ‘global’ settings are; hence, you can use this expression map to deal with the piano stave independently of everything else.
The main one that’ll matter for piano is the “Natural” base switch.
Note…quite a few of the base switches are add-ons that just send a CC, and might adjust some of the playback option overrides. I’m not sure if they’ll actually do anything for a piano sound or not anyway when sending those CCs. Experiment with your copy of the expression map…you can even delete the ones that don’t make much sense for piano anyway.
I.E. Strip it all but the Natural base switch. Switches can be ‘disabled’ via tick mark without actually deleting them.
Once you’re done, click OK, and change to your altered expression map back in the play tab.
To do this start a fresh instance of HALion Sonic. Manually change the staff to use it. Set it up with the ‘default’ expression map (velocity based dynamics). Manually try different pianos until you find one you like.
If you have Sonic and the base Sonic Selection content installed, it does have some pretty nice and dynamic pianos included. Some of them are at least easy to ‘gain stage’ directly in Sonic if they get a bit too loud. The S90ES is pretty high-quality emulation of a top selling Stage Piano…core stuff in many pro line Yamaha keyboards and stage pianos out there. Older tech, but it’s still quite good in a ‘mix’.
You can also do a little extra EQ, and reverb if it’s too dry and in ‘front’ of the mix. I.E. push it further back in the mix by gain staging it softer in the main Macro, and adding more volume to the reverb mix control.
If it’s still too punchy after tweaking its many settings directly in Sonic, clone that ‘default’ expression map, and bring down the Max Velocity for the natural base switch.
I forgot to add, that I think you can ‘disable’ base switches in an expression map without actually ‘deleting them’. So many things a piano stave will not need!
For your piano stave, I’d disable pretty much everything BUT the “Natural” base switch to start out with. See how that goes. Deal with your accents/durations/dynamic changes in the ‘overrides’ section of the map for Natural.