Disklavier

My husband has a Yamaha Disklavier.  Before he got the Disklavier, he
used to compose music all the time using Cakewalk and some other gear.
A few years ago, he got a Tascam US-428 Midi board.

For Christmas this year, I'd like to get him a new computer and
something else to encourage him to start composing again.  I know he
wants to hook the Disklavier to a computer.  I already bought Finale,
but what else should I get?  He has an old sound module and the
Disklavier has one built in.  The Tascam comes with Cubasis VST audio
recording/MIDI sequencing software, so I don't think he needs Cakewalk
again.  Recommendations on what else to get?

Any suggestions would be greatly appreciated.

Thanks.
-yvette