I have the 520, A/V-1s and an A/V-C.
From HKs 320/520 FAQ
Question: Can my surround-sound receiver handle a 4-ohm load?
Answer: All Harman Kardon Audio/Video receivers can handle most 4 and 6 ohm speakers on the market today. However, there are some manufacturers' speakers that have a minimum impedance well below the 4 and 6 ohm nominal impedance. In this situation, the receiver will protect itself by going into standby mode. This will not damage the speakers or the electronics, but it is an indication that the speaker in question is not compatible with our receiver. Note: The continued use of the receiver with speakers that cause it to shut down can result in eventual failure of the receiver which is not covered by the warranty.
This faq applies to: AVI200 AVI200MKII AVI250 AVR 110 AVR 120 AVR 125 AVR 210 AVR 220 AVR 225 AVR 310 AVR 320 AVR 510 AVR 520 AVR 8000 AVR10 AVR100 AVR15 AVR20 AVR20MKII AVR25 AVR25MKII AVR30 AVR300 AVR35 AVR40 AVR45 AVR5 AVR500 AVR55 AVR65 AVR70 AVR7000 AVR70MKII AVR75 AVR80 AVR80MKII AVR85
If you don't go with separates right away, the 520 is especially good for adding separates later on. It has amp inputs so you can use the amps you will be bypassing with the separates to drive speakers in another room or for a 6.1/7.1 setup. Pretty versatile receiver! The 320 only has pre-outs for separates and you loose the use of the amps you have paid for in the receiver when going to separates.
I too prefer separates to receivers. I use a 12 year old Parasound HCA-2200 MK-I to drive my A/V-1s. Can you say overkill!
Ronnie