Mounting Triplanar Tonearm to SME 20/2 Turntable

This will result in reduced performance

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"Will"? WILL??? 

Or, "I think it will". Or how about, "According to something I read somewhere it will." Or better yet, "I'm guessing with no real clue that it will."

Apprently someone didn't read the post above. Either that or doubts what was heard and written. Because if it really is so important for the arm to be coupled then why does it sound so much better when its not? And if its really so important for materials to match then why does it sound so much better when they don't?

Another thing I notice, conspicuous by its absence, is any mention of having actually made comparisons and learned from experience. Not one word along the lines of this is based on experience.  Instead all we have is unsupported unsubstantiated opinion.

Right? Right???

Looking at your table and arm, you could take a hole saw and cut some arm mounting blanks out of different materials- wood, acrylic, aluminum, whatever. Cut a slot and you will be able to swap them out without even having to disconnect the phono leads. Make them all the same thickness so you don't have to mess with VTA. If your local guy can help, ask him if he has some scrap wood or whatever you can try this with. Then when you find what you like best have him make you one sanded all pretty and nice.

Take your time. Big mistake everyone makes is thinking they can figure it out or take advice and do that and be done. Which you certainly can do. But you will be missing out. Because this is not rocket science, nor is it even science at all. Or even exact. My arm sits in a hole and seems quite stable and fixed, yet its really just sitting in a hole held in place by its own weight. Probably some wannabee is right now typing away at a post getting ready to flame on me for the impossibility of this sounding any good at all due to the imprecision of the hole slop, inability to ground vibrations, lack of constrained layer damping, or whatever. As if I haven't heard with my own ears how much better it sounds.

Right now is the best time, you can easily experiment with different things as simple as cutting pieces of wood, acrylic, etc and trying them out. Anything from tape to clamp to a screw or two, anything to hold the arm in place long enough to play a little music. You can for that matter even hear the difference between one screw and two, tight or loose, tape or screw, etc. Guarantee it will not take long to hear what's going on, in fact you will be surprised how fast and obvious it is, and it don't have to look pretty or anything. Try it out, be amazed what you learn. One day, few hours, be ahead of 99.9% which is being generous, as I doubt if even 0.1% have done the kinds of things I'm talking about. 

Why not just drill the hole where you need it??

But yes, tape will be just fine. Possibly maybe even better. In fact the main drawbacks to tape are its a little harder to tweak into position, and then also to remove, depending on how permanent the bond.

My Origin Live Conqueror mounts sitting on an aftermarket jig that makes VTA adjustment easier and more precise. This includes a layer of teflon between the arm and base. It allows the arm to float. Tried it both ways, its better like this. In other words this like everything else you can never assume but just have to try it and see. Only way to know for sure.

In this case you could for example try fastening the arm with the two screws, then try with tape, then if two screws are better go back and add the third. Or not. There is no right or wrong- as long as the arm doesn't go flying off and crashing to the floor!