Disklavier

I'm the original owner of a Disklavier DSC2 Grand with Mark II XG  
control unit.  I would love to have features / capabilities now  
available with the Mark IV series, such as access to content via the  
internet, hard-drive storage, etc., however I'm not going to spend a  
small fortune replacing my entire piano to do so.  There must be  
alternatives to upgrading.... I hope.  It irritates me that Yamaha's  
upgrades are seriously limited and don't allow migration to successor  
series. Maybe they finally got it right with the Mark IV, but that  
doesn't help me.

I'm new to this forum, so have several questions to ask.  I greatly  
appreciate any replies.

a) I would like to play Piano Soft + Audio, or Smart Piano Soft  
media.  Is adding the DCD1 module the only option?

b) If yes, I understand the DCD1 is no longer manufactured by Yamaha.   
Will there be a successor unit?

c) Does anyone have experience in using a PC / or Mac connected to the  
Disklavier in order to play MIDI files, or PianoSoft, PianoSoft Plus  
titles? If yes, I'd greatly appreciate any tips.  I have both Mac and  
PC machines I could use.....

d) Lastly, has anyone used Garageband (Mac) to send data to the  
Disklavier.  I understand Garageband requires a plug-in in order to  
enable Midi out.  Again, if anyone has experience with setup, any tips  
would be appreciated.

Thanks in advance for the help.  I hope to return the favor some day!

Regards,

Rich Freeman