I went through the same issue but, only with 4 ohm speakers. I ended up with the Onyko 809.
13 responses Add your response
While the guys at Crutchfield may be well informed, I find it hard to believe that your NAD can't handle a 6ohm load. Try it out at medium to higher volumes and monitor it. If the protection circuitry doesn't engage and the receiver does not get too hot, I think you are in the clear until you get the $$$ for an amp if you must.
I'll second Bill's comment. This excerpt from a Sound&Vision.com review seems to third it:
Impedance of the RX6 is a little low but not low enough to cause problems for any decent receiver or amp; minimum is 3.9 ohms at 150 Hz. The RX Centres impedance is a little more demanding, with a low of 3.0 ohms at 200 Hz. The RXFX is easy to drive, with a 4.8-ohm minimum impedance at 2.6 kHz, and a nominal impedance of 8 ohms. Sensitivity of all speakers is about average.
The NAD should be fine.
I also find it hard to believe NAD, considering their reputation, cant handle a 6 ohm load, however, the back of the T 748 and its owners manual state, 8 ohm minimum. Sounds like the guys at Crutchfield are well informed. Im thinking different A/V receiver or speakers, unless someone at NAD thinks its OK.
Look up the owners manuals(usually available from their website) to any you're considering. Then see what their manual says. If they have a picture of the receiver in the manual, look at the ohm rating printed on its (receiver) back by the speaker output terminals. That NAD you mentioned does say 8 ohms minumin on it the back of it. This may save you some time and headaches.
A couple of years ago, I may have said to give it a try. But anymore, there have been a lot of complaints about newer receivers shutting down. They do have a lower ohms dip. Stereophile did a review on these speakers, and HERE is a link for their test results if anyone wants to see it.
Once again, Stereophile confirms (excerpt from link, above);
Its impedance (fig.1) remains above 6 ohms for almost the entire audioband, with a minimum value of 4.5 ohms at 165Hz. As well as being usefully sensitive, the RS6 is also an easy load for the amplifier to drive: textbook requirements for a speaker that will be used with inexpensive amplification.
NAD may want to cover their ass with the 8 ohm warning, but it's almost impossible to believe that this speaker will stress the power amp in the NAD. I'm sure that there are examples of (nominal) 8 ohm speakers out there that will be tougher to drive than these.
If NAD has a reason to CYA, then its only true with a few of their products. Most of the A/V receivers are rated for a minimum of 4 ohms. Looks like the amp stage is NOT the same for all of their receivers.
Stereophile link is for the RS6, and speaker in question is the RX6. As stated previously, the RX6 drops to 3.9 ohms/nominal 6 ohms. Then add the RX Centre with 3.0 ohms minimum/nominal 5 ohms for home theater, and the T748s reliability is compromised.
Disagreeing with a manufacturers recommendation is just asking for trouble.
My bad read on the model # in the linked review (I assumed the link was for the speaker in question). Tls also makes a good point about disregarding a recommendation.
However, not all nominal 6 ohm loads are created equal, and I'm sure NAD's "CYA" 8 ohm warning is designed to minimize the likelihood that the T748 might see a really rough patch from a nominal 4ohm speaker. The RS6, per the review, looks to be a very benign load. Given the common provenance of the RS and RX, I kind of doubt that the RX6 and it's center/side companions would be a problem for the NAD, but I certainly cannot say that for sure, so...
as Tls points out - it's not entirely without risk.