Need help adding new codes to your Slingbox, this is the place to ask. You're welcome to ask general Slingbox questions here, but be aware that most of us are not Slingbox experts.
There is no Volume control. Sling have always intercepted the Volume buttons and use them to control the Volume of the Slingplayer and never passed them to the device. So there is no point in having a Volume control on the remote.