Speaker stand height

Why don't you ask PSB how they are ment to be leveled, if you feel uncertain?
PMC for example, says tweeter should be over ear level and mid in ear level. Barefoot says tweeter should be in level with ear. My former MA PL 300 sounded pretty different if i changed level at them. Point speakers towards ceiling, well, you get reflections from ceiling to. Damping a ceiling often tend to make a calmer more mild frequency response.
I would go for the copper sand. Entreq build many devices for vibration control and they often use "copper sand".

You must know where the acoustic center of your speaker is. It may be the tweeter in the 2 way, or the midrange in a three way. This should be the ear height level.

Then the distance between speakers should be the distance to your ears-an equilateral triangle. A nice long metal tape measure work great for this.

Mass is your friend in stands; hollow metal or wood can ring a lot, adding its own a resonant frequency to the speaker output. Knock on the stand with your knuckle and hear if it rings. If yes, dump it. Try concrete blocks if you don't have anything else and hear the difference.

Brad

I have heard that it is ok if the tweeter is above your ear level ,but not below. Is this true?
Todd

Isn't it important to optimize speaker height for bass response? If you get floor bass reinforcement and bass cancellation right, you can then, if needed, tilt the speaker so the tweeter is on your listening axis (assuming that's the correct orientation for the individual speaker).

-Bob

Sit in your comfy listening position, have someone measure the distance from the floor to your center ear. That is the height of your focal point of your speaker. Average is around 38 inches. Your PSB's are designed so the focal point should be the center between the top of the woofer cone and the bottom of the tweeter cone, That spot is the focal point of your woofer. In the example of 38 inches, that spot between your woofer and tweeter would need to be 38 inches off the ground.
Use a laser pointer, adjusted on the inside of the cabinet level with the focal point, turn your speakers in full tow making the laser point at your ears. Imaging should be excellent. If you have a brightness, start turning your tow outward exactly the same on left and right channels until sound is smooth. It is possible that at some point you may start losing center image, or dips in frequency, so stay keenly aware of image and frequency responce.