Interesting discussion. To my mind, in some sense I think even if you're still building a stock or modified BH kit, there is still a pretty large aspect of this that is still in the realmof design, and that is what's involved in putting the system as a whole together. Now for some, this means just getting the basics together -- source, amplification, speakers, and connections, and leave it at that (which is perfectly acceptable, btw.), but for others of us that means, for lack of a better word, tweaking and/or "voicing a system" to our tastes and what we want out of a system. This always seems like the most work, potentially the most frustraating, and ultimately the most rewarding -- when you get everything working just as you want it and working with the room you are in, or other overruling considerations, such as a headphone system if that's what you prefer or can manage in your living situation.
As for me, I like it all, from choosing the amp and speakers as a starting point and then filling in all the other pieces from there, building the components, etc., and then finding/building/modifying the parts to achieve the whole. It's often an interative task, is not for the impatient (or those who simply have other priorities) and can cost some money, though that too can be managed with some sweat equity when you have the appropriate skills and/or are willing to try and learn.
Anyway, I'm rambling, buut I hope I've made the point that even if you stick with just stock BH gear, there is a system design aspect that is still there and can be a large part of the process.
-- Jim