Long winded post, but I'm new to the forums so I figured I'd detail the whole situation.
Just got the vehicle a month ago and mostly loving it, though as I'm sure most here are aware, the BOSE makes a decent mediocre system, but sucks hard as the "luxury" system that BOSE likes to pretend it is.
On my last car (2002 Hyundai Sonata) I replaced a few of the speakers and head unit myself to get a bit more out of the system, but nothing crazy. It wasn't too hard as the media systems were definitely a lot simpler back then. This time around though, due to some extra cash I want to give this car fairly close to "the works" so to speak. Nothing too insane but definitely something that smashes the POS that is currently in there.
Others would definitely call me an audiophile, as I'm one of few people I know left (especially within my age group) that keeps a large library of local media and 90% of it is lossless, with the last 10% being mostly really obscure stuff or free releases that were impossible to find without lossy compression. I actually enjoy a broad range of genres, 40s-10s with some occasional dips into classical, but my top spot is reserved for bass heavy (more so in depth than volume) EDM with Dubstep being the obvious main course (yea yea say what you will XD). So for me at least, the really muddy lows and low-mids of the BOSE system absolutely crush the experience of listening to much of my library. When I'm in more of a 90's 'Lithium' mood or feel like spinning The Beatles the system isn't as noticeably poor but still leaves much to be desired.
Anyway, if I was just going to replace speakers and the head-unit as before I would do it myself, but I'm definitely looking to have a true sub and quality amp installed and given various stipulations that involve the car being partially a gift, I would rather just have a professional shop that some of my family/friends have an excellent track record with do it. Additionally, I'm not going to touch the headunit on this one as its so heavily tied in with the car (especially considering the personalization options that seem to only be changeable through the head unit) and after I installed the AA retrofit kit I've found it to be fairly satisfactory other than the touchscreen killswitch Mazda flipped, though hopefully AIO can work around that eventually.
That being said, for me the most important thing I want to achieve on is avoiding all the Achilles heels of the current system. As I understand it, the BOSE amp does all sorts of manipulation that tries to squeeze the most out of their cruddy tin cans, including sending only mids to the rear speakers, only lows to the front door speakers, and keeping the bass somewhat limited as the you raise the volume. Given that I'm keeping the stock headunit I most likely can't get around its most likely 'meh' DAC, though from other's experiences I should be able to still manage significant gains by using quality aftermarket monitors and solid 5-channel amp that is capable of its own processing.
So here's the big reason I made this thread:
I had originally envisioned that the BOSE amp would be replaced entirely by the new 5-channel amp, but after my initial talks with the installer they explained that given how integrated the existing amp is with the headunit that they will need to tap a signal off of it (I'm not sure if they would go for pre-amp or post-amp) to provide the input to the new amp. Now, I totally understand that non of you can speak for this installer in particular and what approach they will take, but ASSUMING they do it "correctly" is it possible to install a new amp this way and keep the input clean/quality? I've read a bit into how this can be done with a Hi-Lo converter, a summing function using multiple inputs (to essentially rebuild a clean signal from the post-amp/processed BOSE output) on an amp that has its own processing, or a few other techniques. I just want to make sure that they rest of my system won't be handicapped to any significant degree by being behind the BOSE amp like this.
From the few other posts I've seen where others take this approach and the wiring diagram I found for the BOSE amp this does seem like it can work out fine if done correctly, I just wanted the opinions of others who are more familiar with the audio of this car, and ideally, those who have done similar installs themselves. If so, has anyone found what they feel to be the best way of using this method for this car specifically or even in general? I wouldn't mind understanding my options a bit better so I can discuss them with the installer given that this is the first time I'm doing major audio work on a vehicle.
Also as a related aside, has anyone had good success doing sound deadening on this car? Its not too loud at lower speeds, and not even horrible at higher ones, but you do have to raise your voice a fair bit while on the highway from wind/road noise with a tad of engine noise. I wouldn't mind having it be a bit quieter on the highway so I don't have to put my music quite as loud and can improve the longevity of my ears haha. Essentially, have people found it to be worth the effort? If so, what were your main modifications? I have seen this talked about a bit on this forum so sorry for asking again.
Assuming it is done correctly and involves the proper hardware, will taping a signal off the existing BOSE amp (pre or post amp) result in a clean/quality signal for a solid new 5-channel aftermarket amp? Is it even possible to replace the BOSE amp outright?
Again, sorry for the length and thanks for your time.