Dear Joseph: First I will try ,what is my opinion, to answer your very first questions: no the extra arm don't affect the quality sound reproduction ( at least I never detect any effect about ), what certainly affect the quality sound reproduction is the arm holder material.
Now, maybe if I explain some of the why's I have so many TT/tonearms/cartridges could answer almost all your questions ( btw, Tinman: first than all I'm a music lover and second an audiophile and my reference always is the live music not audio devices. ):
the realtionship between the tonearm and cartridge is critical and unique. There are several tonearms out there: unipivot, dual pivot, ball/magnetic/gyroscopic/air/gimball/etc, bearings, tangential or pivoted, different construction materials: titanium/ceramic/aluminium/steeel/wood/hybrid/magnesium/boron/etc., etc., fixing or removable headshells, different internal wire: coper/silver/hybrid/etc, etc, etc.
with all these differences how can I choose or how can I know which is the right one for my cartridge?, we can't for sure: the best that we can do is to buy that tonearm and see what happen. Fortunatelly almost all the tonearms ( the top ones ) perform extremely well with different cartridges, but my need is not only a tonearm that works well with my cartridge: I WANT THE TONEARM THAT HELP TO MY CARTRIDGE TO PERFORM AT ITS BEST, nothing less.
You can't do it with one tonearm/cartidge combination ( only if you are very lucky ). For example: someone with the Triplanar VII and the Universe or Allaerts or any other top cartridge, can say that his tonearm/cartridge combination is a great one ( at least, it is what he heard or think about ) but he don't know if the RB1000 or the DP6 tonearm could perform better with that cartridge and this is what I'm looking for: THE BEST TONEARM FOR THAT CARTRIDGE, not only a very good one.
If we can have several tonearms then we can test the cartridge/cartridges with each of those tonearms to find which one is THE ONE. How can any find it with only one tonearm?, not possible. Now, these are some subjects about tonearms, there are other ones that are important too but that I left for another time.
I own and owned so many cartridges because each one has a different signature sound. Almost all top cartridges ( MC and MM ) in the right tonearm perform flawless with any kind of music recorded, all put me very near to the live event and give me a very high emotional level of feelings. I don't choose " that " cartridge for Pop music and " that " cartridge for Jazz and " that one " for classical. I change the cartridge because I want to hear a little different sound ( like a whole, not more bass or better high frequency or more deep in the soundstage ). I can live extremly happy with any of the tonearm/cartridge combination that I already find: I'm not finished about and time to time I learn so much things testing my big analog choices.
The audio rules like the resonance frequency between tonearm/cartridge ( 8Hz to 12Hz ) can't tell us the whole " history ", that audio rule is only a subject to start. When someone speaks that the linear tracking tonearms are better than the pivoted one because the tangential ones has no " error " and track exactly in the same way that the cutting-head recorded the LP or that the linear tracking tonearms does not need AS, these statements means nothing real about which tonearm is best: THE BEST TONEARM IS THAT ONE THAT TAKE MY CARTRIDGE TO PERFORM AT ITS BEST, IT DOES NOT MATTER THE TONEARM GEOMETRY/BEARINGS/MATERIAL/INTERNAL WIRE/ETC/ETC.
Of course that you have to have a good platform ( TT ) to try your combinations and the more important analog audio device in the analog chain: a Phonolinepreamp up to the task.
Btw, I have to design my own Phonolinepreamp because what I try out there can't meet my audio/music targets. Right now we are in tonearm design and amplifier one.
My Phonolinepreamp has two totally independent phono stages, so I can switch only two tonearms at the same time.
There are many subjects to speak about tonearm and cartridge findings. I think that every one of us can write a book about with different experiences, all valid, and different opinions. Here are mines.
Regards and enjoy the music.
Raul.