I bought the Selekt Edition with Katalyst Line Out a year ago; I did demo the Organik stereo at the time as well and bought one later….
I have three types of the four modules here although obviously only running one at a time through my Selekt Edition via a Lineout Stereo module. The DAC modules I have are Standard(DAC 1), Katalyst (2) and Organik Stereo (3). I tried them in turn again only last week.
The standard DAC is very ‘polite’ but not particularly dynamic nor has a great soundstage; doesn’t resolve complex passages (prog rock, symphonies) particularly well but fine as a background or introduction.
The Katalyst is definitely a step up, good soundstage and with other parts of the system (power, interconnects, network etc.) addressed can sound very good - better or equal to many DACs out there - deals well with the complex passages of music
The Stereo Organik is excellent, deals with complex music passages and has an excellent soundstage even in passive and with good speakers. Listening to it now with a single NC250 (new to me) and my Serhan&Swift Speakers it doesn’t leave much room for improvement without spending a lot more.
There are a few Linn Selekt users who have gone with Dual Stereo Organik Power Amp modules but have discarded them in favour of external amps (NC250, Akurate 4200, Klimax Twin) to get better control over the speakers. There are also some that still prefer the power amplifier modules in Exakt/active with Kudos or Linn 119 / 150. Makes for a neat single box system.
Having heard the Dual Monos at my dealer I would say the Monos improve on the Organik features even more, but the improvements become increasingly marginal. The mono line out cartridges may well have better optimised pre-amp modules leading to the improvement - the DACs also have a different less powerful FPGA (quieter?).
The standard modules are very cheap in the usual places(so I bought one online for £60!), and the Katalyst can be had now for 40% of the list price…
My recent decision process was to try two power amp modules with two Katalyst into Kudos Super 10As at home with a view to going Exakt/active, but I preferred to spend the upgrade cost on a single Stereo, i.e passive, Organik DAC module. I sold the Super 10As only this week to retain my S&S Mu2s, for now.
So Selekt provides many options and rabbit holes too.
Best to demo at home and negotiate with the dealer commercially as well.
@PeakMan may also wish to contribute too