Can SMPS based preamps/amps sound organic ?

but I always seem to hear some kind of switching noise which comes through as "digital" sounding.

hmmmm.....I wonder if you are imagining this? How did you trace/pinpoint the "digital" sound to exactly the SMPS in the preamp/amp?

I wonder if there are any designs using SMPS that can actually sound natural and organic ?

sure! At RMAF2013 I heard the Rowland 625 driving a Raidho stand-mount & it sounded very good. For the limited time that i was in the room on Sat & Sun I could not find any obvious faults. I, of course, discounted the fact that the Raidho, no matter how good, could not reproduce deep bass.
There’s been rave words said about the Merrill Veritas amp which also uses a SMPS power supply. If I'm not mistaken Bel Canto Black is another example.
There must be many others out there.....

SMPS used for convenience?
Maybe. At one point i was talking to a well-regarded engineer at a class-D amp manuf & was informed that SMPS in amplifiers are just about coming into their own. Their fault, as you stated, was high(er) output noise for audio applications. We already used SMPS in other audio applications such as cellphones as the audio quality does not matter as much (different application & diff specs). I was informed, by this engineer, that the highlight of the Hypex NCore N1200 amplifier module was its SMPS. And, the final goal for any class-D amplifier was to use both a SMPS power supply + SMPS amplifier module.

I'm doing well. thanks for asking. I see that you are also doing well & growing by leaps & bounds as an audiophile. :-)
thanks for your feedback, Pani. Now your original comments make a lot more sense. Would have been nice if you had stated all this in your 1st post to give all of us a background where you were coming from. ;-)
anyway, it looks like we have a variety of opinions on this topic from several owners & listeners..... 

kijanki,
Roger Sanders makes a regulated linear power supply for his Magtech amp which can drive his ESLs. Here is the link to that white paper:

http://www.sanderssoundsystems.com/technical-white-papers/161-the-magtech-regulated-power-supply-wp

And, i believe that he has a patent on this power supply architecture....

welcome Kijanki.
the Magtech regulated power supply looks like a switching regulator but it is not a traditional SMPS (like the kind used by Rowland, Linn, Benchmark, etc) but it looks to me that it is some sort of Pulse Frequency Modulated (PFM) switching regulator - it monitors the pulsating waveforms out of the regulator & the rail voltages (it seems that the system has some knowledge of min rail voltage & max rail voltage & what the acceptable ripple should be) & when the rail voltage goes below the min, it multi-pulses until the rail voltage reaches the max & then shuts off. Cycle repeats when the rail voltage falls below min. 

2ndly, it seems that the Magtech power supply is very much like the multi-voltage used by ARCAM in their class-G amplifiers. see this link:

http://www.arcam.co.uk/ugc/tor/a49/Class%20G%20Explained/Class_G_the_ultimate_amplifier_technology_150714_A.pdf

the Magtech regulated power supply looks like a class-G PFM regulated power supply......

Hi Almarg,
please see this blurb that appeared in Stereo Times in 2013 that clearly says that the Magtech regulated power supply is patent pending:


http://www.sanderssoundsystems.com/latest-news/219-january-2013-sanders-magtech-amplifier-receives-the-stereo-times-most-wanted-components-2012-award

Almarg,
found 1 patent application for Roger Sanders re. ESL loudspeakers (not the regulated power supply):


http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4&p=1&f=G&l=50&d=PG01&S1=sanders-roger$.IN.&OS=in/sanders-roger$&RS=IN/sanders-roger$

Thanks for the clarification, Almarg.
The fact that the 2013 patent application (I believe it was 2013 & not 2003) has not issued seems par for the course. I had one patent application issue in 2015 when it was filed in 2011. 
Re. the 'patent pending' on his Magtech regulated power supply - not finding any patent application or issued patent is a mystery indeed....
Like you wrote - maybe he never pursued a patent & the other press is now old & written words cannot be retracted today?