Trying to boot linux distro on a media streaming box

Although I have little experience of these devices myself, you may well be able to install Linux, depending on the actual brand and model of the device.

I'd recommend that you check out the freaktab and slatedroid forums to see if people with similar devices to your own have provided instructions as to how to install Linux/Android ROMs.

 

.pkg is a file extension, ergo a set of three letters which can well be meaningless otherwise. I am sure there is no relation to pkg files used in Solaris, OSX or other places.

You may try simply renaming them to .zip, or .jar or .apk and see if you can extract them.
Google Play store is not strictly speaking part of Android, just like say the gmail application
Though I think software ought to come in .apk files still. A useful example of an alternate "store" or repository is F-Droid.