I purchased 4 ohm speakers (Dynaudio Focus 110) and was prepared to use my HK AVR 635 to power them after getting H/K's approval. I connected them and could tell immediately that the receiver was going to struggle to handle the load. I had an Adcom amp that I was able to immediately use to relieve the receiver of those duties and was amazed at the difference in sound quality. The receiver couldn't come close to the bass that the amp was able to produce. My point is that any of those receivers may be able to handle 4 ohm speakers, but consider an external amp to get the most out of them.