I don't know if others have already know this, but I just figured it out it was so simple.
(1) on iPad you need app called OPlayer HD.
(2) on your HTS make sure have default * user enabled, so you don't have to type in username and password while you streaming and changing channels.
(3) In OPlayer HD, select open URL option in File Server menu on the left.
(4) then gives URL such as http://your.server.ip.address:9981/stream/channelid/505
Then you are done.
Currently my iPad2 can't really handle the HD channels, because of graphics processing power is limited. But I am sure people with iPad 3-4 should be able to watch them smoothly.
Enjoy it