Upping DIY speakers nominal ohm load (newbie)

[Tin Ear *BA*]

Gentlemen
I need some help with an upcoming project. I'm looking into doing a speaker project similar to the "Noah's 8s" project listed on the Parts Express site.
These speakers are being built as a gift for my son and the amp he will be using is a Yamaha RX-750 which is set up for speakers nominally rated 6-8 ohms.
Well this project lists the nominal load around 4 ohms. How does one bring the ohm rating up so the amp will be comfortable with the speakers. I was going to use the crossover designed for the project but if anyone can guide me in a way to up the ohm load I would appreciate it.

My experience in the DIY speaker arena has only been in car audio (sub boxes). This will be my first attempt at anything for the home. (Don't let my son know I'm using him as a guinea pig :W ) If all goes well, I think I would like to attempt something along the lines of the Natalie P for myself.

By the way, any other advise you would be willing to give a "newbie" would be hugely appreciated.

Thanks in advance.

[ThomasW]

Sorry but you can't safely raise the impedance of a speaker system unless you use very expensive transformers

Look around for a system that uses a 8 ohm woofer if that's all the Yamaha will drive.