buzzing from speakers

If you don't have anything damaged now you will. Why not to use portable humidifier?

Inputs (and outputs) are protected to human body model 2kV/2ns standard at best. You can easily get tens of kV on your body in dry room with carpets.

Assembly houses that build boards for many manufacturers have very stringent static control. Everybody is grounded all the time (wrists and shoes) and grounding test is mandatory for every employee in the morning and after the lunch. It is of course possible that they do all of this just to impress me.

Static not only can damage but also change value of components (precision resistors).

Ryder - It depends what you're touching. If it's grounded case then chances of damage are very low. What if you connect and disconnect something and touch input (or output). Even if you discharge yourself by touching ground or grounded case you might have to go to another room (phone call) and charge yourself back walking on the carpet. I found post on Audiogon where somebody damaged speakers by strong static discharge to TT arm. Again - most likely it will not happen but why to risk your investment. Portable humidifier is a very inexpensive (and healthy) way to prevent the problem.

When somebody tells me that you cannot damage SS gear by static I want to ask this person if he is willing to pay others for damage if he is wrong.

As for the hum - how loud is it? When did you notice? (was it sudden?). Have you changed anything (plug to different outlet, add component etc.)

Pickup from the speaker cable is not very likely. In order to get electromagnetic pickup you'll have to have source (transmitting cable) in order of tens of MHz for 2m speaker cable (2m cable is 1/4 wave antenna at 37.5MHz). Capacitive pickup is possible but you would notice change just moving the cable.

Ryder - "Believe" is the right word. Static might zap the input (or output) if you touch it even if you turn equipment off. Damage to speakers was just an example.

Analog Devices application engineer told me once that they had problems with customer's A/D converters loosing linearity after being zapped by static. To me it is even worst than damage (that can be repaired).

You don't need to open case to create static damage. Even with properly grounded equipment it might happen if voltage is high and it is repeated many times. You'll find testimony of that here on Audiogon forum. I am able to destroy prototypes of industrial electronics zapping them few hundred times with 10-20kV zapper to heavy metal case that is grounded directly to copper ground rod (not the flimsy inductive 3th prong). It is not issue of "IF" but rather "WHEN". Situation of repeated static discharge is unacceptable.

It gets much worse if you touch something else than case - like metal knob sitting on the metal shaft of the volume pot and not touching case (small gap). Or even better zap speaker wire (and I assume that grounding is non-inductive and perfect).

If you read more about static damage - one of the first thing advised is humidity control. You'll find many posts of people who damaged their computers by strong discharge to a case.

Stay amused!