Romy - I've thought about this one for some time.
Let's just dismiss equipment business due to the declining industry sales trends, tight margins, and painful design/production/marketing logistics. And I don't see you selling audio equipment at a store (or to stores as a wholesaler). That leaves consulting.
From your perspective, some obvious consulting problems and some examples come to mind right away. This list needs to be refined but it is a start:
1. PERSONAL -
* Expanding hobby to profession risks diluting hobby's fun factor. Biggest personal hurdle
2. DEFINITION OF OBJECTIVES WITH CLIENT- re">
* Perhaps the biggest professional hurdle
3. OUTSOURCING OF CONSTRUCTION -
* Imagine a San Francisco client wants you to design and build dedicated room + system. The logistics of sourcing design architect, construction, electrical, permitting, etc. in a new state might be painful. Might be fun depending on your personality. Think about the mid-bass horn project at home. The logistics will take a lot of time away from the core sound project
* Of course room design is incredibly subjective. I think that expensive "acoustic" room at Goodwin's looks great but sounds terrible; how do you avoid that result in a room size/shape you outside your experience?
4. PROPERLY ADDRESS CONFLICT OF INTERESTS TO MAXIMIZE PERFORMANCE -
* As you well note, "consultants" usually have back door deals with hardware suppliers (e.g. consultant takes vig (margin) on equipment sale, construction etc.) Whilst the consultants initial intentions may be clear, there is pressure to move equipment sales move towards best "margin" vs. best "performance
* Perverse incentives of hourly billing agreements and fixed fee billing agreements (e.g. never complete project vs. complete too quickly)
5. COMPLETION DEFINITION-
* For project completion (final billing), how does one objectively assess the success of a system implementation?
6. MARKETING -
* Not really sure how you could start marketing this, other than posting on your site
* Actually keeping the customer's names confidential, it would be a good exercise (and interesting to others) if you posted progress-photos of consulting projects as they moved forward. That would be good marketing
==> FINAL THOUGHTS (FOR NOW) -
In the end, I think you need to keep this close to a fun hobby as possible.
One path is highly customized, ground-up, system design/consulting/implementation. These projects likely cost (significantly) over $100,000 dollars. Fixed fee + overruns might be the proper billing mechanism. Maybe you could aim for just a few very high end projects per year where potential clients are given the opportunity to listen to your room and sound philosophy beforehand, then agree to give you an extreme level of design freedom.