Upon serious consideration this is a much more challenging topic than it appears at first blush. I think those of us that rely on our audio systems for musical pleasure, rather than for purely sonic thrills are looking for a system that will allow us to more easily connect with their music on an emotional level. For me that has occurred twice in my 30+ years as as a vinylholic and audiophile; when I began all of this at 13 and assembled my first "serious" system, and at the beginning of last year when I acquired my latest stuff. I'm sure that my initial period of contentment was due to my having few preconceived ideas and being totally jazzed at being able to play my music, relatively full range for the first time. My latest spell is the result of a quantum improvement in my system such that it now possesses very few limitations. Therefore, I conclude that I have spent the better part of 30 years attempting to replicate the "surprise" that that first system provided, and I had to wait that long to put something together that transcended my normal expectations of musical pleasure. The lesson for others may well be that the path of the audiophile is one of foolishly questing for the unattainable, and not entering the search for "better sound" is the wiser choice. I think the more valuable lesson is that great things are worth the work and the wait.
So where to start? Used is good. No truer words have been committed to this site. Without knowing how big your room is and how loud you like to listen its difficult to make anything other than generic recommendations based on my taste. However, I will say that while I like the turntable and speakers, and the Mac stuff is okay, I've never been a fan of the Adcom 555. I have found it to make voices sound distant and canned, and highs to sound wiry, particularly strings. The bass is potent though, as you've noted. The Vandy's have the capacity to play full range with real authority with the right amplification, but they really, really sing with tube amps. You might want to look at a Van Alstine modified Dynaco ST70. The original is from the 60s and 70s and is one of the most popular amplifiers ever made, so they are relatively easy to find. The problem with the originals is wooly bass that is not particularly extended, or tuneful. The Van Alstine mod banishes most of this, and makes a great mate for the Vandy's. They are also pretty cheap. Good units go on sale on Audiogon for much less than $600. I have heard this combination in several systems and have found it unfailingly musical. Good luck!