What is the most overlooked consideration?

Experience from my professional life. Once the original owners / developers move on or sell out, don't bother anymore with the brand. Passion, vision all disappears in the corporate cookie cutter, sell as much as you can world. Quality and service levels disappear, and often the brand too. 

@aewarren absolutely WAF!

@freediver Your question is very difficult to articulate a reply to.  I will take a chance on being judged mentally infirm and attempt to explain my process, expressed as recommendation or steps to judge musicality.   Since this is intimately subjective, the process others use will differ.  

First, develop your impression on how live acoustic and amplified music sounds in intimate to concert hall venues.  The only caveat is that large arena rock, while it has the ability to evoke much emotion, normally has interfering distractions and distortions, and I do not recommended it for this process.   Make mental notes on how the composition and performance evokes emotions in you, and how the sound in the venue contributes to your experience.  Also gain an understanding of the sound of studio recording techniques, for studio recordings present a different perspective from the concert hall experience.  Identify recordings where the engineering techniques are evident, and where they contribute to the emotion expressed by the composition and performance.  
 

Second, identify recordings that bring memories of the sound of live concerts you attended and more importantly, evoke similar emotions you felt at live concerts. Also, identify studio recordings where the engineering techniques are evident and they contribute to your appreciation of the album.  I have some favorites … 2L Recordings MAGNIFICAT - Nidarosdomens jentekor & Trondheimsolistene, Anita Brevik; Stockfish Records Katja Werker feat. Gert Neumann - Contact Myself 2.0: Live; Mercury Living Presence Saint-Saens, Symphony No. 3, Dupre (organist) Pray, Detroit Symphony, Led Zeppelin (1).  

Third, find a good dealer and make an appointment for a long listening session.  With electronics, I usually get agreement to bring my model to hook up in their system and evaluate their model head to head.  It’s work, but worth the effort.  For turn tables and speakers, this is not feasible.  In these cases a good, confident dealer you have a relationship with will have a return policy, permitting you to evaluate in your home.  
 

Finally, compare the equipment on the basis of the command it has over the composition and performance (musicality) and its ability to evoke emotions.  The usual audiophile criteria of timbral accuracy, dynamic response, resolution, leading edge, image density, staging and imaging play their own important part in evoking emotion, and an equipment’s musicality cannot be separated from these usual criteria.  However, try not to focus on these individual criteria, but rather, focus on the sum of all performance criteria as musicality.  You will know when the magic occurs and you feel the emotion of the composition and performance. 

I agree with @ghdprentice that musicality includes the properties of rhythm & pace and midrange bloom but as I stated, it is an intimately subjective criterion.  I consider timbral accuracy first and foremost, then the ability to reproduce the nuances in tonal and dynamic inflection, including secondary harmonics and ambient decay, as well as image palpability.     I guess these are more specific attributes or subsets of rhythm, pace, and bloom.  

Synergy because the best piece of gear will do anything coupled with the wrong one...

 Once bought...

Adressing the three working dimensions:

Mechanical :   Speakers vibrations resonance controls...(other gear vibration is important too but  secondary compared to speakers)

Electrical :  Wall plug and central panel control of interferences...

                    But mostly overlooked , the necessary well  grounding of dac, amp and preamp...

 Acoustical:  the system/room various parameters control...  Balance between diffusion,reflection,absorbtion and control over these ... What is very overlooked is the power of the Helmholtz resonators by their parameters adjustment and their location to tune and tame  a room...

@jsalerno277 

Agreed, there are other sonic aspects that must be correct as well.