HD2 firmware on my ASUS O!Play Air HDP-R3?

[r3_user]

Hello,
I have a few questions regarding HD2 firmwares on an R3 player and sorry if the questions are noobish!

My current boot code is 23 and my firmware is 1.21P

1. Why do people install HD2 firmwares onto an R3 player? I always see people talking about it but I just don't know why they do it.
2. Does my boot code change if I install a different firmware? (For example after I soft reset my firmware to HD2 1.12.06rev4?)
3. I installed the HD2 1.12.06rev4 onto my R3 but I had difficulties to see my network folders. When I selected "network" the only folder I could see was the default "my shares" one. Is there any way to solve this problem? I don't have any network problems with firmware 1.21P.
3. Can I also use the official firmware release 2.02 for my R3? Is it better because the version is newer?
4. I can't get my .srt subtitles to work. My R3 just refuses to show them ):

Thanks a lot in advance!