New to stepmania, questions on difficulty and sound options

Howdy, i have been searching around google unsuccessfully, i apologize if this information is commonly found somewhere and i missed it.

I have installed and am running stepmania 5 without problems, but i have a few concerns

1. I have 5.1 surround sound that the game is clearly not utilizing. How do i force it to use 5.1 surround?
2. Is there a way to move the arrow track to the middle of the screen instead of offset to the left?
3. The step precision needed for comboing is substantially harsher than DDR. in DDR i usually miss maybe 1-5 steps per song and in stepmania i am missing a huge chunk of steps according to the scoring, and i am getting tons of bad/good notes, whereas in DDR i frequently got perfects and flawless. Is this adjustable or tweakable?
4. Is there a collection of american pop songs anywhere? i have scoured around and found a handful of singles but im looking for normal everyday songs you might hear on the radio.

thank you for any help!

1. SM only supports 2 channels, you'd have to rely on your audio drivers or speakers for more.
2. Center 1P in UI or Theme options
3. SM's timing is actually a lot easier than DDR... arcade DDR, at least. Either your global offset needs adjustment (sync calibration in options) or you can adjust the game timings in advanced options.
4. They're out there, although I don't know where.

Zenius-I-vanisher's user-contributed simfile section seems to have a ton of relatively recent pop music. Dance Anarchy packs usually have a bit, and r21freak might have some as well.