What would be the weakest link in this setup

I think all your gear is plenty good enough. I'd look at the room. Is it well treated in terms of damping? Are the speakers well placed for smooth response, precise imaging and adequate bass? Treating the room - especially damping the first reflections and overall echo - is crucial for sound quality, and is the best bang for the buck you could possibly get with your current system.

I'd say your room. Your ceiling is 8' and width is 16. A multiple like this will make bass modes much worse. Bass traps at a minimum. You'll be amazed at the improvement in sound. Like the above poster states, room treatment. Until that is done it really doesn't do much good to try different components until your room acoustics are done as well as you can get away with. The "average" room has a frequency response of plus or minus 15db or more! No snake oil, hard facts of physics. The sound improvement by taming the room, if you can, is very substantial. You'll hear the improvement big time. I suggest going to realtraps.com and rives.com and reading. With those dimensions you have a serious problem in your bass and that will muddy up the mids and highs. Cheers

It always is a safe bet that the weakest link is the room, followed by the recording. Spending $40 on The Master Handbook of Acoustics, and another $500 on DIY treatments, will trounce any equipment or cable upgrade. If you just have to spend more, throw in another $300-500 for an RTA to really do it right with some actual measurements if you are new and can't/won't fully trust your ears. It might also help you optimize the integration of the sub with your mains - usually another weak point in a system. Then another $500 worth of very good recordings and new artist discoveries, with a modest allocation towards your favorite adult beverage if you are so inclined.

All the above will give you many many hours of involvement, education, enjoyment, and sense of accomplishment. Consider the road less traveled. ;-)