Can I expect to pay full retail for a new system?

Mitch4t,
large purchase, 15% to 20% off list.

Remember, this is YOUR money that you are spending, so if you are smart enough to negociate a better deal, good for you. (Don't worry about the dealer, they'll take care of themselves! If they don't like the offer, they'll refuse it.) I don't think etiquette is really an issue, as this is business.
Typically, you can expect a 10% discount or so, especially when buying an entire system. (However, depending on the dealer, you can sometimes negociate even more. As an example, my friend negociated a higher discount on a set of very high end mono block amps ($20K retail and he got them for $17K out the door.)
One thing to consider is that your standard B&M store has a high overhead, so they have a slimmer margin, versus say a dealer that operates out of their house (such as the one my friend dealt with!).
Now, if the dealer comes to your house to setup the system, and fine tune it, then the discount might nothing, or very little, as they are not only selling you a component, or a system, but providing their time and expertise as well.

My two cents worth.

In the old days, a full complete system, came with appropriate cables gratis.

I think it's up to you and the dealer in question. A discount is a realistic possibility, and I think a realistic expectation, with the type of money you're spending.

When I was a newbee to the high end, I had the impression that it was not cool to try to barter. After all, these were "high end", nose in the air, lots of attitude types. They didn't barter like the unwashed mass market hucksters. They were above that. Besides, you were expected to pay more, that's what paid for the "service" you got from them.

Fortunately in those days, I couldn't afford to buy any high end gear anyway. How some of those dealers treated me when they found out that I coudn't buy at that instant is another thread.

After a while, I discovered that some dealers didn't have high end attitudes and were actually nice, helpful people. As long as you didn't waste their time when there were paying customers in the store, they were willing to invest some time in you knowing that you might come back in the future when you were ready to buy. It's called relationship building. I appreciated that. There are some people whose products I would gladly pay a little more for in return for what they've provided me in service and in education. And if you were close to a purchase, expecially if it involved multiple items, then they often initiated the suggestion of a discount, especially if it was a package deal.

So I think that the dealer is a critical variable. Some will offer a discount. Some won't. Find a dealer you like and whose advice you trust. Get to know them and let them get to know you. And you will find that deals will emerge.

My experience with gear in the 5K - 10K range is that 10 - 15% is automatic and you can probably get more. If you are lucky or have a friend you might get 30%.