Weakest link

I think you’ve already nailed it. It can be virtually impossible to confirm what the actual weak link is until you’ve made (usually) at least Some sort of substitution.

Sometimes even rudimentary substitutions can be rather illuminating on a given problem...and sometimes can only cloud the issue further. The real trick is, I think, as you have done, is to try to identify the exact nature of whatever sound problem you feel you have and then to try to work backward, by way of substitutions, toward uncovering what one component item (or more than one...or even several - yikes) that is responsible. Sometimes I’ve found that continuing to make substitutions (for various other reasons) had "improved" the one particular problem I’d had in the back of my mind without ever actually making it go away...only to finally hit paydirt and find the true cause to be elsewhere. Then again, on a different sort of problem, a similar series of substitutions may act to actually audibly unmask the underlying problem, making it even more irritating. In the long run of having futzed around with all that over the decades, Either of those two scenarios, either the unmasking of or the covering up of a problem, can sometimes be useful in the diagnosis process and anything like that can help reduce it all down to the next likely suspect.

But, yes, without a doubt, it is most often like trying to pull at a sweater, especially when things seem to be, as you say, sounding pretty good and pretty well balaned to start with.

The real question may be how much the original problem is bugging you and exactly how far you might be willing to go to squash it. Not an unrealistic or unworthwhile question to pose in this hobby at all, I’ve found.

ivan, that's very thoughtful. Yeah, when the system is operating as a whole and especially when operating already quite well, how to separate the contribution of each element and each interaction.
In another, this time hypothetical example, if the music has insufficient drive pace and flow, I would look at the source before anything else.

If you will let me add, Inna, to what I posted above. All in all, what I’m saying really, is that this likely a ’stage’ that everyone seems to get to with their system and is often not to be taken lightly if one wants to successfully navigate through it, IMHO. Many people do not foresee this last step as being even necessary when they fully get into system building. You research your components/wiring/room/etc and make your purchases, install and set everything up, listen and tweak some...and then you’re done, right?? Except that a lot of times it may be necessary to go back, based on some perceived problem(s) that never got satisfactorily resolved, and redo some things...maybe even some very basic things...like component choices...(although not always that, of course).

But, I think this why I tell people to always try to learn from their mistakes from system building. I suppose I’m of the opinion that too many folks, once they feel they’ve made a purchasing mistake, may just pack the thing up right then and there and send it back without a second thought. Without fully wondering what the real nature of the mistake in their mind, or the equipment, actually was.

And when you get to this ’final’ stage of problem solving, all you really have to go on are your audio instincts...and if you have not done your ’homework’ along the way and have been passing up all your opportunities to sharpen your instincts, then you can really end up being stumped at this last stage and really have no real sense of where to even begin.

There’s no reason not to just dive into it really, but it’s just that (IMO, anyway) this stage of the game is not likely going to prove to be something that can be ’played at’...that is, that it seems to me to be unlikely that most folks will be able to just dabble with it and fix their perceived problem(s) on the first try. Sometimes you see people in this kind of boat on forums who are trying to get someone to help them out and basically do this for them online. But, it can be so very difficult to help them at this point because it is such a hands-on kind of thing - and that’s really what a person’s own audio instincts are for...the trial-and-error process that hopefully eliminates the person’s problem and not their wallet.

Just sayin.

As to your hypothetical about the lack of drive, yes, my own instincts would be to at least consider the source unit.

For dynamic issues, I might look to passive crossovers first, either their design or their parts quality, or even consider going active.

OTOH, I once had a setup that had a very relaxed, breezy kind of sound. But, it was soo relaxed it lost a sense of purpose with bass lines. Changing amps, as it turned out, to a nice, clean, tight signature was just what the doctor ordered.

Thanks for lettin' me rant above, Inna...not that I give anybody much choice. ;>)