Hello Ecka,
This is a link to a more technical explanation of the signature upgrade to both the DAC and transport.
http://www.emmlabs.com/html/press/release.html
May I suggest getting in touch with Jonathan Tinn for more information.
Ecka, I think it depends on what vintage of the CDSD you have if a SE" upgrade is warranted. I bought mine originally in July of 05. It was one of the first ones with the brushed aluminum face plate and no clear coat. It had the new transport and the port in the back for future software upgrades. Not quite a year thereafter I had to send it to Andreas Koch for a problem I was having with drop outs on some of my disc. When it was there he did all updates to bring it up to the current SE" version. As far as I know, he did a software update and he also updated the power supply to my unit. It came back sounding noticeably better!
A short time later I sent in my DAC for SE" upgrade. I'm elated to report that IMO the SE" upgrade is NOT subtle.
Within all of 3 seconds I knew this was special. First I heard a much more realistic rendering of texture of tone that made all instruments just sound that more vibrant of their each own individual character. Also, immediately noticeably was the sound space, it was much wider and deeper. Resolution of low level detail was just fantastic as I heard things I never heard before. Dynamic shading is now more startling, it digs deeper in the lows and high end
extension is improved as well. It is more detailed and yet at the same time more relaxed in the presentation which sounds more natural and less electronic in nature. It got better with break in for awhile then leveled off in improvements for quite sometime. Then after 3 months or so I got yet another improvement concerning bass definition and extension. Needless to say I'm thrilled with the SE" upgrade to the EMM duo. Overall it just pulls me into the music and the musicians intent more than ever before.
Whatever you decide I wish you well and hope you find what you are looking for.
All the best,
Tom