I have had the opportunity to audition a few of the mentioned alternatives in controlled comparisons. In all cases they were played for other people who work in the Hi-Fi store I work full time at (Overture Audio in Ann Arbor, Michigan, USA) and for any interested customers in the time I had them. There has been full agreement by all who listened as to which were the more tuneful and musical pieces.
I did not care for the Khan nor the Karmen top plates. They gave an artificially detailed sound to the music while compressing the music, damaging the flow and not allowing you to hear as far into the mix. With the Khan I also found emphasized surface noise. The Karmen was better than the Khan but that just means it was less bad compared to the stock stainless steel top plate. I have not heard the aluminum plinth/top plate combos, but considering my findings on top plates and plinths (more below), and the fact that Linn built a prototype for such a thing a decade or so ago and didn't feel it was worth bringing to market, I don't honestly have a lot of interest in them. But I would certainly evaluate one if the possibility presented itself.
Plinths are a different story and are actually the only third party piece for the turntable I felt made an improvement in the tune (I don't include cartridges or arms in this). But this is also an area fraught with complication. I have had a Booplinth here and did not find it to be a musical improvement. It wasn't bad but was less tuneful than a stock Linn plinth. The other plinths I have evaluated are all solid hardwood plinths built by Chris Harban of Woodsong Audio or supplied by Linn. I have found in general that the Woodsong Audio plinths are musically superior to most stock Linn plinths, especially current Linn plinth woods. Indeed the best sounding plinths I have heard have all been made by Chris, but there are defintiely differences in musical perfromance of different woods, and also there are differences even between plinths of the same species of wood. Although I have found that you can generally expect a certain level of performance form a specific wood made by the same craftsperson, there can be some exceptions. After all, wood is not a precision material with completely consistent characteristics so there is always going to be some variation.
In my experience the Woodsong movingui plinths have been the most musical with cocobolo a close second and curly maple and wenge not far behind. I believe that Macassar ebony is probably up with cocobolo and movingui but I was not able to do a direct comparison. An original Linn Rosewood plinth with large corner braces, refinished using the same wiping varnish Woodsong uses would also be somewhere in the top group - I believe better than wenge or maple but not quite up to movingui. Other plinth woods from Linn would generally be below those mentioned above. I have sold a fair number of movingui and cocobolo plinths as well as a few curly maple and wenge and a few others that are still good but rate a bit behind the top ones. All the purchasers have been quite happy with the improvement to the tune and musical quality the plinth brought to their LP12, not to mention the quite stunning looks of most Woodsong plinths.
I spent a lot of time evaluating a number of plinths and trying to find something that correlated to musical perfromance: weight, density, hardness, even measured resonance characteristics, but none of them helped. In the end the only reliable way to know a top range musical plinth is the musical quality of the tone it makes when it is tapped. The problem here is that you need to have tapped a bunch of them and heard the variations to get a good idea of what works (this is why I am pretty sure about where the Macassar ebony would fit as it had a beautiful tap tone). In general what you want to hear is a tone that is musical with a good range of tone and a little ring but not too much. A lot of ring translates into a forward upper midrange that sounds artificially more detailed but can be a little fatiguing, a tone with weak bass will sound that way in the system (black limba), a tone that rolls off a bit in the highs sounds like a subtle high filter in the system (wenge) and a dead or hashy tone is not good at all. You can find a great deal more about this in the topic I created about the sound of LP12 plinths here:
https://www.lejonklou.com/forum/viewtopic.php?f=3&t=294
The biggest problems are getting a Woodsong plinth as he is way behind in supplying them, and also there is the occasional outlier. An example: I have a customer who paid me to drive to Virginia and do complete strip downs and setups on a couple of LP12s for him. (I ended up setting up a fair bit more after he heard the improvement the precision torques made to his Radikal PS unit. He also ended up buying a set of Sagatun Monos after hearing what they did to his Klimax Kontrol!) He had three plinths we needed to check out to decide what to put on his primary and secondary LP12s. Two were from Woodsong Audio, a movingui and one I hadn't heard of before, a catalox. He had tried the catalox himself and didn't like it, finding it hard and bright. I asked if he had done a tap tone test. He had and reported it sounded like a bar of steel! Not good. I did some checking and found it was a quite hard wood that could be used as a substitute for ebony. His third plinth was a fine-tuned Linn afromosia. When I went out there I tap tested all three. Catalox was as described, rather hard sounding. The movingui was good but not as good as most movngui I had tested and the afromosia, which I had generally not been happy with previously, was the best of the three. However, this customer worked with highly skilled woodworkers and he had one very precisely true up the afromosia plinth and refinish it. I believe this is why it performed so well. So the afromosia went onto his best LP12, the movingui on the other and the catalox went way somewhere.
Hopefully this gives you something to go on as a start.
