Forget about the size of power cords - go look at an arc welder to see if size matters.
Understand the way sound / power works - it's logrithmic. Doubling the power will give you a "just noticeable" difference in sound volume. But for a doubling of sound volume you'll require 10x the power. So, to respond to your question, 15 additional watts won't do Jack (small j or big J?). Multiply the receiver's power times 10 to get a substantial effect.
You're thinking about 50 watts to the tweeter and 100 to the woofer, without any way to balance? 50 watts to a tweeter (without going through a crossover) is pretty sporty - good luck.
Have to recommend like Elevick that you think this through first. The Carver by itself may be better than using the HK at all for the fronts (does the HK have pre-outs?)
For $500 you could get one of the Denon's or older "high-end" Yamaha's (I used to have a DSP 3090 that was pretty good), that should be able to make fun of the HK, and not have you running aound doing weird things with you amps.