As much as I love the Martin Logan's, they really aren't suited for what you are looking for. The Sources/Purities have a VERY limited dispersion, and they sound their best in a very limited sweet spot. As such, if you are walking around, sound quality will be noticeably different then if you were sitting. The same goes for moving to the left and right. That said, in the sweet spot, the ML's will provide a sound that is fantastic for the price, and will work very well for both HT and music.
As such, the Vienna's will likely work better in this situation. I have a pair of the Mozart's, and I strongly recommend moving up to the Mozart's over the Bach's. You likely will not change these speakers for at least ten years, and the additional cash is well worth it for the quality increase. Keep in mind that the VA's are extremely power hungry. I'd highly recommend using a separate amplifier and pre-amp. Based on your choices, I assume you are shopping at a Magnolia HT store. I'd get a receiver from them, and then grab a amp elsewhere, either online (Outlaw, Emotiva, etc.) or from a high-end dealer (Rotel, Anthem, Krell, etc.). The VA's do require power to make them sound as good as they can. I'm running them off of a Pioneer Elite VSX-91TXH, but I did try them on some Primare separates, and the quality difference is very noticeable.
It really depends on what you're looking to do here. If you think you'll spend a lot of the time sitting down and listening to music, I do strongly recommend the ML's. The VA's will be superior for classical music, but I do feel that for all other genres, the ML's, when in the sweet spot, are hard to beat. However, based on what you've said, sounds like the dispersion of the ML's won't work out very well.
If you do decide to do the ML's, I STRONGLY recommend the Purity's over the Source's. The extra $1000 gets you two 200W class D amplifiers built-in, really alleviating the need for a very high-end receiver. I've found that I recommend Source's to customers that have existing high-end amplification. ML's do dip down to low ohms, and do require good, clean power, which would be tough to get without spending quite a bit more then $1K.