Dimmers in a Listening Room

Years ago this used to be a problem for me. There are two issues: line distortions making their way into your system (electrically), and mechanical noise caused by the alteration of the line voltage/current waveform. Mechanical noise can be heard as ringing filaments in the bulbs, as well as moderately loud humming transformers in your system.
In recent times, I successfully used dimmers with the following guidelines: (1) you're lucky if your light circuit is different from the circuit driving your system. That's probably the biggest preventative measure for issues. Given that most people recommend a dedicated circuit for a high-end system, I'd install one even if you didn't use a dimmer. (2) Go for a good quality dimmer (usually $30 or more). The cheap ones can throw lots of noise on the line; some of the better ones have a soft turn-on, which seems to be kinder on bulbs. (3) Make sure you have the right dimmer type for the lamps. Low-voltage lights that use a transformer require a different dimmer (read "more expensive") than incandescent line voltage bulbs. And there are different types of low-voltage transformers (magnetic and solid-state), which require different dimmers, too. Using the wrong one causes filament ringing as well as transformer noise. (4) Good quality bulbs can tame any residual filament ringing. 
In my experience, good line-level incadescent dimmers can be found at home improvement stores. Low-voltage dimmers are harder to find, but can be found at specialty lighting shops and can be special-ordered from places like Home Depot.

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