Level the floor

The only item which MUST be level is a turntable, and that is usually easily fixed.

Right.  This floor is not flat.

As discussed (and, okay, discussed...), this is some serious tilt.  I wouldn't want to have a desk that tips this much.  Okay, so, stick some books under the desk -- 'tis the way -- but sound-making machinery is prone to Surprises and I didn't want to learn that I'd solved this the dumb way when I heard a bang.  So, I asked.

Turntable: pucks.  Huzzah.

Speakers: I wouldn't want to run those on a tilt either.  Call me picky, but this set is modular, irreplaceable, with some heavy magnets at the top, and this much tilt makes me nervous.  I also want to be able to adjust them, the floor is carpet, that can cause surprises, and and and.

I've learned, for which I'm grateful.

OP:

Each issue has it’s own fix. Speakers often have adjustable speaker feet/spikes which can be used, as well as speaker stands with adjustable feet.

Stone countertop places have all sorts of scrapes around. Find small pieces they will never sell. 

mrj OP

I was assuming the speakers would be forward from the back wall, to place them on the very gradual portion of the floor. Thus, shims ought to work.

In any case, I believe speakers should be tilted back so that the tweeters are aimed at seated ear level. This will involve tilting, usually accomplished by a block or riser in the front.

In my case, concealed by the lower ’skirt’ I have attached a 1-1/2" block in the front, the 2 front wheels attach to it, thus the rear single wheel, with no block, keeps the rear of the speaker 1-1/2" lower. Blurred, hard to see, bottom of image

Easier to see, 9th photo here, as well as the speakers in-place tilted

https://www.audiogon.com/systems/9511

My heavy speakers can be on wheels, lighter speakers can be on ’skid’ plates, allowing alternate toe-ins

KLH OEM stand tilted their speakers back 8 degrees

JBL Speaker Stands

For Klipsch (they made their OEM ones also)

Custom, get smaller speakers higher and tilted