I have been frequently auditioning speakers for the last 20 years, many have impressed me, and some of them I bought for the quest to great sound. All I can say, is that None will give you the perfect answer to your question: "Which set of speakers would provide the most detail and maintain a good balance of highs/mids/lows?"
However they can get you pretty dam close to perfection, out of the speakers I have auditioned recently within your budget, I have been incredibly impressed by the following in order of preference:
1. Reference 3A Grand Veena (They are a bit above your budget new, you can get them used if you have patience) these are for me the best speakers I know in that price range and well above it. They have also won all kinds of awards and are frequently compared to 15k+ speakers. They are also very sensitive, so you could use a SET amp or low power tube, but also respond great to power. Overall, nothing I have heard bellow the price of my kharma's has impressed me so much, and I have heard a lot.... Natural, transparent, balanced, powerful, intimate, lush, liquid, passionate, huge soundstage, depth, dynamics.... they give you all....
2. Quad ESL-2805 (or better the 2905's used). The 2905's were the final contenders for my current setting, and were competing against the Reference 3A grand veena and my kharma 3.2fe which retail at around $25k, that reference can hint you in how good these two contenders were. These speakers are a beauty, they dont go so low, are a pain to place and need good amplification, but all these suffering is worth the amazing transparency and mid lushness. Many have referred to these as the best loudspeakers made regardless the price, a bit exaggerated but gives you an idea of how well regarded they are. These ones are breathtaking with jazz, classical, vocal but also rock, however, if you are used to high volume levels, they might not be for you. The 2805's have the same sound signature as the 2905's and only sacrifice volume and low-end extension, they are also easier to place. As a note, these models are far superior to the classic esl63's that are often praised here.
3. Verity Audio Finn (or Rienzi used). These ones are also incredible, and have been the ones with the highest WAF of all the ones I've had home. They disappear effortlessly, are highly efficient, and as with the Reference 3a, you could use low power amps to drive them. This is a very natural and balanced speaker with amazing transparent soundstage and lush mids. These two models from verity set a very high standard of built quality and sound, plus their signature voice is to die for...
Ive heard the MBL, and when amplified well it made a good impression, but not enough to tumble the ones above, as for the focal be, i would skip them, you can do much better for the price. Seriously consider these 3 choices, they might be harder to audition since they come from small companies, but in this case, smaller companies produce better quality and are more passionate about their products, its really worth to check them out, 6k is a lot of dough... good luck,