Need to set up product with multiple units, multiple attributes

I have three products set up -- a 3-bar sampler, a 6-bar sampler, and a 9-bar sampler. I want the customer to be able to choose any combination of 7 different flavors when they order one of the sampler products. I have already entered the flavors as attributes.

How do I:

1. Set up the individual products so that the customer has to order 3/6/9 bars (depending on the sampler size). I do not want them to order 4 or 7 or 11 or any other quantity.

2. Allow the customer to choose which flavors to include -- in any combination, i.e., 2 of one, and 1 of another; or 6 different ones; etc. The flavors are showing up in a drop down box, but right now there is only one choice regardless of whether there are 3, 6, or 9 bars in the product.

3. Set a fixed price for each sampler (i.e. $18 for the 3-bar; $36 for the 6-bar; $54 for the 9-bar). I do not want to price per bar because we don't sell them individually.

I keep seeing references to "set mixed to on" but can't find this anywhere and searches on the various forums produce nothing useful.

Thank you,
Lisa in Vermont

Since you're not selling by individual bars, just make that clear in the text and have an option name of Sampler with values of 3-bar, 6-bar and 9-bar, each priced at its full price with a prefix of blank instead of +. In the product creation page, set to priced by attributes. The price will show as "starting at $18".
Make one of the sizes default; if you want, add an option value of "Select size" and make it display only and default so the customer can't forget to choose.

Probably the most effective way of allowing full choice on flavors is to have nine flavor option boxes. Name them something like 3-Bar (1), 3-Bar (2), 3-Bar (3), 6-Bar (4), 6-Bar (5), etc. and include a default value of none or the most popular, as you wish.

Brilliant -- that did it. Many thanks!

Lisa