You were trying to change surround levels, forgot to ask why?
I'm wondering about that too.
OP, what do you mean that you can't adjust the surround volume? During setup you can individually adjust the volume of each speaker. During playback your master volume controls all speakers equally.
Now, everybody likes what they like. I'll tell you that since almost all audio recordings are mastered in stereo, (2 channels only... front left & front right), that's the way most of us prefer to listen to music. When you add surround speakers, you lose the effect of the music sounding like it's coming from a stage in front of you. But if you have a room full of people, (a party), adding the surrounds means you can normalize the music volume so it's not too loud in front of the room and too soft in back of the room.
Surround sound is generally used for TV/Movies, and the audio in most modern TV shows and movies is mastered in a surround mode... usually "5.1".
You have 4 of the "5" in "5.1". They're your Front L&R, and your Surround L&R. The thing you're missing is the Center. It is unfortunate for TV/Movies because maybe 90% of the sound in TV/Movies is mastered for the Center speaker. Think about it this way. Every sound in a TV show or movie that is supposed to originate from something happening
on the screen, will be mastered to the Center speaker. If somebody on-screen is talking, their voice comes from the Center. It would be weird if you saw something happen on-screen, but the audio came from behind you.
If you don't have a Center, those sounds are split equally between your Left & Right. If you're properly balanced, this will indeed provide the audible illusion of the sound coming from the middle, thus it's called using a "phantom" Center.
The other thing you're missing is the "1" in "5.1". That is the subwoofer. Many of us consider one or more of these critical. The "1" is a separate channel just like "Left" and "Right" are separate channels. It gets a signal called Low Frequency Effects, (LFE). These are the booms and rumbles in explosions and monster stomps that shake your chair and thump you in the chest. But in addition, a subwoofer helps greatly with normal bass that is difficult for all but very expensive speakers to produce.
So think about what you want. Mainly music? TV/Movies? Just you? Parties? Chest thumps? All of it? Trust me, we'll be more than happy to help you spend your money! (Just kidding.)