I'm not a tech and figure only you guys might know the answer to my questions . . .

I understand that 2 companies make products that essentially turn acoustic pianos into the equivalent of a Disklavier, with most of the bells and whistles.

Does anyone make an after-market product that does far less, meaning it does not accept discs and does not turn into a player piano but simply, like a Yamaha "Silent Piano," allows a person to use headphones and shut off the acoustic sound (for playing late at night, in an apartment building, etc.)?

If so, who makes it, what does it cost, how well does it work, and does its installation cause any problems?

Thanks in advance for a reply!

Here you go:

http://www.gabor-pianos.co.uk/

This is the kind of thing I was asking about. Thank you for the link.

Is it available in America? If so, any idea how I could get to see/hear one?

Contact them. Do some homework.

OK.

In less than 3 weeks, I'll decide on whether or not I'm getting a Yamaha Silent Piano. If I'm happy with that, then it'll become a mute point. I'm hoping so, because even though it's expensive, getting a factory installation would be totally care free, especially given the great repuation Yamaha has in this particular regard.

However, if, for example, I just fall in love with the sound of something other than Yamaha that A) I can afford, and B) is not available with a "silent" system (headphones), then I'll contact the folks in England as you say, find out what I can, and report back here. Thanks again!

Another thing to consider is the grand piano muffler. It doesn't shut the sound completely off, but it mutes it by about 50%. It is a much less expensive than a true quiet system, but the advantage is you still have the complexity of an acoustic sound.
http://www.grandpianomuffler.com/

There are 2 companies in the US. PianoDisc. and QRS. I have installed a few of both and prefer QRS. Neither are perfect. They can be fiddly. But they work for what your are wanting.