In a high-end system, every component can have really good specifications and by itself sound fine. But when added to your system, it either reveals that it is or is not the weak link. If it is not the weak link, the sound of your system improves.
If it is the new weak link (the sound of the system degrades), the weak link may not be the new component but rather something else and here is where the process of finding out where the weak link actually is gets a bit sticky.
It is easy to assume that since you swapped out the component, the new component is the problem. However, there are other sub-links in this chain that may be where the real problem lies. Think about what these sub-links are for a moment. What about the interconnects? Did you have to relocate the component when adding it to your system (physically rearrange the gear)? What about the power to the new component (is it plugged in to the same or different place)?
The point is this: there are other issues that may contribute to the degradation of the sound. Finding out where the problem hides is part of the fun with this hobby.
I am working long distance with a person to remove hum in his system. The complaint was, "Every time I listen to the music ripped on my PC through my speakers, I hear hum." So where do you think the weak link is with just this amount of information? Not enough information? Maybe. Some of you are already theorizing what the problem is and have arrived at a few options. Let's look a bit deeper.
This person has a PC (media server) located in one room and this hum appears whenever this source is selected in any system in any room. Aha! Multiple playback systems from one source. Are you getting closer to finding the weak link? I hope so. Let's see what else is going on.
The PC runs a playlist that every remote system can then select as an input source. Whenever that input source is selected, the hum appears in that system. Any more ideas? I'm sure that you have one or two at least. You should be getting closer. Need more data? OK.
The PC sends the digital signal through a D/A converter and then that signal is distributed to all of the other systems in the home as an analog signal. You should have nailed it by now, or at least identified the sub-links.
In your opinion, where is the hum coming from?
It's the distribution system (this is the sub-link). But where in the distribution system is the actual weak link? What is the source of the problem? Is it the cables, the splitters, or what?
The problem is two-fold: the distribution system and the house wiring. Low-level analog cables that run long distances are prone to picking up hum when run parallel to house wiring. The method for distribution of this signal is the problem and solving it may require changes in the way the system is configured.
The point is this: what appeared to be a problem with the component (here the PC) was in fact not where the weak link was at all. The problem was the way the signal was sent from the PC to the other systems.
I'm sure that you have run into similar issues with your own system and found later that the weak link was not what you suspected it to be. This is why our foreheads are flat; its a genetic hand-me down from all of the times your ancestors have found their weak link. Every time they found the problem, the palm of their hand would smack their foreheads and they would think "I was so stupid; that's where the problem really is!" Countless repetitions of this AHA moment throughout the history of mankind have caused our skulls to flatten at the forehead. And we all have flat foreheads so we all have had or have had ancestors that have had many, many of these moments when we felt so stupid.