Your logic is not incorrect since the amps in your receiver will no longer be drawing much power, but it's definitely not a problem. Using a receiver as a pre with a separate amp will draw a bit more power due to the extra power supplies & whatnot, but it's absolutely nothing to worry about.
In fact, the only way you're even slightly likely to have a problem would be if your home and electric wiring are SO old and poor that you blow circuits on a regular basis, like when you run the coffeemaker and microwave at the same time -- and in that case, you need an electrician anyway. If that's not the case, you have absolutely nothing to worry about. I used to have a small recording studio set up in my business partner's basement, in a row home (that's what we northeasterners used to call them, they're "townhouses" now lol) in Philadelphia. This house was at least 30 years old and we KNEW we had electrical problems... Ceiling fixtures that occasionally worked, wall outlets hanging loose (it was a scary place)... But I ran a huge Mackie console with a huge heavy rack mounted 220 watt power supply, a big rack of outboard gear, 3 multitrack recording machines, keyboards, a QSC pro power amp and who knows what else -- all on one 20 amp circuit. It was the only good circuit in the basement, being a newer one they had put in for the washer and dryer, but we never had a problem.
Especially in your system, you are WAY within electrical limits. Those B&Ws are small, efficient speakers and a fairly easy load, and won't draw much power even at high volumes. Plus the 1075 is only rated at 120 watts/channel anyway, not a very power hungry amp. My engineering partner runs a 1095 AND a 1090, plus his big CRT TV, an SVS PB12 Ultra/2 sub (1000 watts) and the rest of his system, on one dedicated 20 amp circuit without a problem, and he's driving Dali Helicon 800s across the front and B&W DM604 s3s for surrounds!
Bottom line is, don't worry, you're fine.
BTW, two small thoughts. One, I have doubts that you'll actually hear much difference on your speakers with a new amp. I'm a huge proponent of overkill when it comes to power amps and using one or more separate amps is never a bad idea. The reasons I say this are that HK receivers have a rep for having excellent built-in amps (haven't heard any of them myself), plus your speakers are so small and efficient that they're probably getting plenty of power from your receiver already. However, if you're considering upgrading your speakers, which I think will make more difference than a new amp, you'll definitely appreciate a separate power amp at that time anyway so it can't hurt to invest in one. (You didn't mention your sub... upgrading to a really good sub might breathe new life into your system too, so consider that.)
My other suggestion is to consider the Emotiva LPA-1 from
www.emotivaaudio.com before you spring for the Rotel. Rotel makes very fine amps and they're not at all a bad value, but the Emotiva has got to be one of the greatest values in audio today. I'm very familiar with the Rotels and I own an LPA-1 and I can tell you the Emotiva sounds absolutely as good as the Rotel amps, is built like a tank, and costs a lot less at $500 shipped with a 5-year warranty. Not to mention it's more flexible since it can be used in two different configurations: 125 watts/8 ohms x 6 channels or 125 watts/8 ohms x 5 channels plus 2 x 50 watts/8 ohms x 2 channels. Just something for you to consider.
