A quality receiver won't have a problem with 4 or 6ohm speakers. The problem is most cheap cheap or even midfi receivers don't have a big enough power supply and adequate cooling. Even a halfway decent separate amp will handle these speakers with ease.
The energy speakers aren't close to being vintage but they are pretty nice. They made the assumption that you have some good equipment to run the speakers. So it was a design choice to answer your question.
If I were you, I would buy some nice separates instead of receivers. You can find some great deals at a good used/new stereo store. Plus they usually offer a 1-2 year trade in value of the priced that you paid. For example, buy an used amp for $200.00, a year later trade it in for some other piece of equipment and get $200.00 trade in value.
Happy Listening, the Prisoner