I can help.....
I'm a Jamo dealer (however I don't support the line a whole lot anymore) and can help you with the products you listed. The "A" in the model number designates the series that you've selected for your front L/R and rear L/R channels. That is their mid-level product in-wall. The "K" in the center channel you listed means that it is from their Kevlar series which uses a different type of driver for the midrange. These will all integrate together fairly well. Just a heads up: The center channel is of higher quality and will sound a bit different from the other four. It's not possible when using the A's because they don't make a dedicated center channel in the series, but it is best (not mandatory) to use speakers of the same quality/series for all 5 or 7 speakers in a home theater. I always viewed the "A" series as Jamo's step up distributed audio speaker and not for a home theater. This is because they didn't support the line with bi-pole/di-pole surrounds or a dedicated center. Jamo's "K" line is what they really intend for people to use with movies. I would not recommend using another 660-A2 for the center for two reasons. 1: When sound disperses out of the center channel it will be extremely narrow and easy to locate; 2: You usually have to buy them in pairs which means you will have an extra one left over.
The "A" line will work for you, but with some compromises. If possible, build a back box behind each speaker and fill it with acoustical foam. Call Jamo, ask for Marcus in tech support and ask him for the recommended back box size for the different models. Don't listen to the infinite baffle stuff. These speakers will sound better with a box behind them.
My experience has been that most in-wall subs are not very good (I'm being generous in saying that). However, there are some great ones out there if you know where to look. Triad, Phase Technology, RBH, and even TruAudio make some excellent in-wall subs. I would NOT recommend using the Jamo in-wall sub for a movie system. It makes noise, that's for sure, but not the kind that you would enjoy during an exciting scene in a movie. I highly recommend investing in a good subwoofer in even the most basic home theater. A properly engineered in-wall sub can be expensive, particularly compared to a cheesy one. I work with home theater gear for a living (including the Jamo in-wall sub ONCE - that was all it took) and without a doubt in my mind you typically get what you pay for with in-wall subwoofers. If you could forgo the in-wall sub and get a conventional design you would have a lot more options for less $. It is NOT important for the sub to be of the same manufacturer or line as the rest of the speakers as I stated earlier. It's perfectly fine (and in most of my systems normal) to use a different brand for the subwoofer.
As a whole I would say these speakers are OK. To be honest, my experience is that there are more unique and better products out there for the money.
An alternative system that I would highly recommend is from another European company called Canton. You can still stay in the same ball park as the Jamo product (under $400 difference going by MSRP). Canton’s LCR in-walls are a great product for your front three and MSRP at $350 each. Use their 5¼” in-walls ($430 per pair) and you should be all set. A good in-wall sub is going to be a significant step up in $ from the $320 the Jamo 10” will run you. Keep in mind that with the Jamo you still need to add an amplifier which their MSRP is at $300 - $400 depending on which model you choose. Phase Technology makes a fabulous in-wall sub. The whole kit including the amplifier and back box runs under $1300 MSRP. These are just my experiences with the product and type of set-up you are asking about. I’m sure there are others here that will have some input for you that is maybe different from mine.
