Why not the piano as a reference for bass

While I can agree that no speaker system can fully capture the sound of an acoustic piano, at least within the context of what I have heard from sound systems, Yamaha has carved out something different with their top level Clavinova instruments.  These are not trying to reproduce the sound of a piano recording in the context that is normally contemplated.  Rather they were conceived to produce (as opposed to reproduce) the sound of a piano.  I have heard the result compared to Yamaha's C7 and C9 and the result is remarkable.  How a Bosendorfer would compare I cannot say.  The standard was Yamaha, not Bosendorfer, so presumably the difference would be obvious.

With all due respect to billstevenson, there have been so many attempts for decades to come up with a substitute for the acoustic piano that doesn’t need tuning, etc., and Yamaha has been at the forefront with their hybrid, Clavinova, and other models. Yes, they have made improvements in the sampled piano, but it is still a canned sound, not an acoustic instrument. As in a sampled electronic pipe organ, despite the increased resolution, etc., there is still no way to recreate the multiplicity of so many sound sources, no matter how many audio channels and samples are used to create the random complexity of the acoustic instrument. A professional musician can tell you that you can take the highest quality string samples for instance, and that in a simple example may sound good, as soon as you layer more and more, the result homogenizes and sounds less convincing. But if for example, you keep adding more acoustic string instruments, the sound gets more and more complex, and is easily recognized as far superior to the canned samples. It has to do with the infinite number of variables in individual bowings, vibratos, intonation, and many other factors. Also, we are trying to convert this enormous complexity into an electronic signal, reproduced by audio transducers. The fact is that we’re conditioned to believe that the sample is the real deal in live performance, Broadway shows, and recordings. I maintain that I can take a child and sit them in front of a real cello, and there will be no question of how they will respond to the physical affect of that instrument as opposed to a recorded sample. 

Well timstella, I would never presume to tell you or anyone else what you can hear.  I can tell you that in one iteration of my life I was in fact a professional musician.  Although I joke about it:  How many musicians are there in a 15 piece band?  Answer:  14 and a drummer.  I was the drummer.  Anyway I always had, and even though with age my hearing has diminished, still am blessed with pretty good hearing.  If you have the opportunity, I encourage to try to listen to, and to play if possible, one of the new Clavinova pianos in comparison to either a C7 or a C9.  You will be astonished.  To change the subject, have you heard a demonstration of the excellent modern stringed instruments compared to the best of the traditional ones such as Stradivarius or Guarneri?  To my ears the only real miss is the viola and even they are really excellent.  Given the astronomical prices of the traditional ones it is a real breakthrough that such wonderful instruments being made again.  And now back to pianos, sorry my mind wanders, Beethoven was limited by the piano technology available during his lifetime.  It is interesting to speculate that perhaps with advances in technology perhaps a future composer will expand the possibilities of piano music yet to come. 

It is evident that nothing beat the organ if we want to test the bass  depth. But there is other dimensions of bass we can test best with a piano.

Bass is a multidimensional band registers set related to timbre in acoustical normal conditions, for this a piano cannot replace an organ, nor the reverse and the tuba is as the viol an indispensable tool.

Music is rooted in timbre perception not in frequencies per se ( as a source of information communicated by the vibrating sound source).

I am not a musician nor an acoustician. It is only what i learned tuning my system/room ...

Synthesizer beats an organ for bass.

All organ bass has a slow attack compared to what can be done with a synthesizer.  And the right synthesizers can go infrasonic, and not just to modulate the audio oscillators, filters, and voltage controlled amplifiers.