No problem. Let's get right into this with some background for the traditional and surround sound systems.
On the OEM surround systems such as the European or even the Acura, they use a better surround processor such as the LOGIC 7. For now, think of this as the same concept of a Home Theater setup. The difference for music, there are some effects such as reverb, echo or a punch of other stuff that makes the experience interesting for music. With these systems that are properly tuned, you hear a wall of music from the front stage L/C/R channels. Many concerts or fixed auditorium systems have gone to the center channel speakers giving a better listen experience to the audience.
Unfortunately, the factory Alpine Premium system does not give you that experience. They use a different DSP from the better vehicles that I mention before and that particular surround processor I am not to fond of. I ripped everything out and started from scratch to achieve the right performance level of a 7.1 surround sound system.
The rear speakers have to different schools of thought. Rear-fill is considered from the traditional system of front & rear and from the complex system of a 3-way front with just midrange speakers in the rear to highlight those frequencies. This gives the rear the ability to hear exactly as the front. With surround sound school of through for the rears, it acts a rear-fill and certain information is steered to those speakers just like a HT setup.
Based on the equipment the shop choose for you, this is a traditional system. Many members here that I give advise to, I ask this as the first question whether you want a surround system that really works or the traditional system. The bad part of the upgrade in the surround system is it will cost you bucks from not to bad to expensive.
If you have no means to hear a proper car sound system, if you do have a HT setup try listening to your favorite music one of the surround codecs. In your manual it will tell you which ones a good for music. Listen in one of the modes for a while and switch back forth to the dedicated stereo mode. This way you can tell which preference for music you like. And that's how you will determine that answer of traditional or surround sound.
I have you ever heard the Focal speakers before? The tweeter can sound harsh and bright with a tinny sound. To match up other components for a surround system to the Focal's will require using other manufacture speakers to make up the center and rear pillar. Another consideration for a surround system to think about. For the rear door, you do not need the extra top end frequencies that a tweeter gives you.
In it's simplest terms, a passive crossover is an external device that is hooked up after the amplifier and distributes power and sound frequencies to the various speakers. Passive crossover's unless they cost over $1k for that component alone will not give the sound quality of the other type of crossover network. The 6to8 falls into that category and it consider the best on the market right now. The 6to8 gets hooked up prior to the amps and it considered a DSP unit that already has a built-in crossover network along with eq and time delay for each channel. The sound quality is coming out of this unit is outstanding.
By using the passive crossovers that comes with the component speaker set, you will not be taking full advantage of the 6to8, IMHO, the 6to8 now becomes an overpriced item. You can use a much cheaper DSP such as the Audison Bit ten series and run the passive crossovers. This will give the same results and sound quality.
If you do go for the traditional system, even better, that money to spend on the 6to8, you can go for a better headunit. In this case, i would go with the Kenwood Excelon 891 or 991. They both have a built-in DSP that give all that you need. The Uconnect 430N or 730 which ever you have is nothing to write home either. This will give you the best sound quality path.
Hope this helps.
Best for now.