Pairing with Vienna Acoustics Hadyn Grand&Rel B3?

No, monos have no inherent high damping factor. They simply yield greater channel separation. The particular amps I am suggesting are also rather compact. The class D technology in these amps does though. If you prefer stereo amp configurations, try Bel canto Ref 500S:
http://belcantodesign.com/Belcanto_Ref500_Amplifier.html
and Rowland Model 102 stereo:
http://jeffrowland.com/M102.htm

G.

Guido- et al. A friend of mine also has a REL and recently has been experiencing some feedback issues. He called REL to discuss and they said he needed to pair his B2 with a Class A or B amp and not D, which he is currently using. The explanation was a class D was not grounded and because of this could severly damage the subwoofer. Does this sound accurate? I ask because the amps you are suggesting are in fact class D and I don't want to ruin my sub as well.

Also, assuming the Class D is okay, would the Bel Canto M300s have enough juice or is the extra $1500 per mono worth it?

JRDG class D amps, and I believe also Bel Canto amps are very much grounded. In fact, users manuals require use of grounded power cords, lest you void the warranty.

I have heard several times the JRDG 312 class D amp connected to a Rel subwoofer, and there was no problem. The system was as quieit as a hybernating mouse. Soundings Hifi Of Denver Colorado routinely features JRDG class D amps matched to Rel subs. 312 is grounded, balanced in the output phases, and transformer coupled for full output isolation.

Never the less, I have heard also of humming problems with some amps.

Here is what the JRDG Model 102 and 201 manual has to say on the subject:

"WARNING: Both positive and negative outputs

are electrically active with respect to chassis
and/or system ground potential. Therefore, this
amplifier cannot be used in certain loudspeaker
switching configurations, such as those used in retail
demonstrations. Failure to avoid these precautions
may short the outputs to ground and can result in
damage to the amplifier and will void the warranty.

Certain subwoofer speakers which derive signals from
amplifier outputs will require additional circuitry to
properly isolate the amplifier output. Please contact
JRDG before connecting these types of subwoofers."

I do not recall if Bel canto amps are also balanced in the output phases and have potential probs with some subwoofers. . . I will check with the factory and will let you know.

The matter of compatibility of class D amps with subs is not set in concrete and depends on individual amps and individual subs. You may need to ask questions specific to a particular sub to the manufacturer of the amp you are interested in.

The difference in price between the Bel canto M300S and the Reference monoblock series is not so much a matter of power output, but of refinement of design and implementation. Bel Canto makes amazing products at great prices. The price difference among their products is a factor of wht these devices offer to the user.
G.

I had an excellent conversation with Matthew at Bel Canto. He explained to me that:

Bel Canto 500 series amplifiers, both Ref 500S and Ref 500M can be connected directly to a Rel subwoofer, because they have only 1 active speaker lead, as if they were old style class A or A/B amps, while the 2nd lead is referenced to ground, which is what the Rel sub expects.

Ref 1000m, and all 300 series amps, have 2 live speaker leads, and if connected to a Rel, they are likely to damage themselves or to damage the sub.

He added that the easiest, simplest, and likely most sonically compelling solution is not to connect power amps to a subwoofer at all, but to connect a line level output from the pre to the sub instead, regardless of what type of amp you use.

Guido