Bell Canto C5i Integrated Amp with B&W Nautilus 803 Speakers. A Question

What is the size of your room, and how much room do you have behind your speakers?

that said, those speakers can be very forward and bright without the right amplification. Mating that with a 60wpc Class D amp is likely not going to result in a bold or warm sound. 

Besides room size, treatment and placement, how loud do you listen? I used to have a BC C5i that I used with ~88 dB efficient speakers (first Spendor SP 1/2E and the Golden Ear Triton 7s) in a medium size room and had no problem listening at average levels of 85 dB or so.  It is when you really want to crank things up (mid-90 dB or higher) that you really need the higher power amps. Remember that watts / sound level is a logarithmic relationship, not a linear one. For example, if it takes you 1watt to hit 75 dB, it'll take 10 watts to hit 85 dB, or 100 watts to hit 95 dB -- in other words, power requirement goes up 10 times for each 10 dB increase in listening volume.

Final suggestion -- invest a few dollars in a sound level meter or sound level app for your phone.  That is the best way to get a good idea of just how loud YOU listen.  Remember that one's person's "moderate" volume may be "extremely loud" or "soft" for others.

Yes make sure it can go loud enough otherwise c5i is a very good sounding and versatile choice.

Thanks alot for your input.

Your amp will be seriously underpowered for the intended application.  Nothing wrong with class D amplification, in fact I prefer it with my B&W along with a tube preamp.  IME 200 watts would be a minimum figure.  
A loud listening level for me is in the lower 80db range with peaks in the lower 90 db range.  Normal listening levels are 5-10 db less than that.  So, the power required is not for head banging sound levels.  The power is necessary for a balanced sound output.  Not enough power results in thinness and over- emphasis of the top end.  I currently have N802 and Concept 90 in two of my systems so I’m not talking theoretically or repeating ridiculous crap like you need Classe or McIntosh amps to match B&W.

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Interesting -- I listen at the 80 to 85 dB level and like the sound of my relatively low-powered Schiit Aegir much better than the VTV class D amp that had 150 watts/ch.  No issues with thinness or an overemphasized top end in my system. Just goes to show that everyone needs to figure out what works best for them, not someone else.

While amp output wattage combined with speaker sensitivity determines overall volume, the performance of the speaker is also dependent on how much instantaneous and unrestricted current the amplifier and cabling can deliver. Higher current will result in the ability to control the speakers better. It is a blanket statement to say Class D amps do not deliver current as well as Class A or Class AB amps, and it is not true for all of them. But the statement is true for many of them. Class D amps were designed to produce power in the most efficient of ways.

Bel Canto’s non-reference class D amps are pretty much unmodified ICEpower modules in a pretty chassis. They handle frequency extremes well but lack the current delivery and filtering to thicken the rest of the frequency spectrum. Pair that with a hard to drive speaker that tends to be tipped up in its sonic signature, and you won’t get a good mix.

If you look at the impedance chart of the B&W Diamond and Nautilus speakers, they all look something like this (I could not find the 803N specifically but I found a few 801N, 804D, etc and they all look similar):

In the chart above, the impedance dips below 4 ohms for much of the lower midrange (100-700hz). Without an amp that has solid current delivery, these speakers will sound thin in these frequencies.

The Aegir on the other hand emulates a Class A amp and prioritizes current over power. While only 20 watts per channel at 8 ohms and 40 watts per channel at 4, it will handle the impedance curves of a current hungry speaker better and enable control and improved tone than the ICEpower Bel Canto, but will not play as loud.

A quick search also shows that the Goldenear Triton has similar dips below 4 ohms, but not as deep and not as wide across the spectrum compared to the B&Ws. But this also confirms why you likely prefer the Aegir over the Class D amp you have.