That's pretty normal if the speakers have a rubber surround...the surround freezes stiff and makes it harder for the speaker to move.

I've found that most speakers sound 'muddy' when they're really cold, but after playing them for a bit they warm up and sound proper again. Just comes with the climate.

 

The problem with ANY high level converting system, whether a $15 Stinger or a $400 JL is you are still taking the amplified signal from the factory deck and converting it down. The speaker outs in factory decks distort so early that, to avoid distortion, one really needs to add an outboard pre-amp system. Plus most factory decks have the auto bass reduction system at higher volumes which bites nut.

The Cleansweep is a decent piece if you can somehow guarantee the volume on your factory deck will never be moved. IMO that's a little unrealistic. The RE-Q tries to correct for the bass/volume curve on the fly and does a decent job. I like it.

Personally, I like using something where I can convert the factory deck into a preamp signal and then add in my own line level signal. Right now I am using an Alpine CHA-1656 line level changer controller that has inputs for the factory deck. It works great.

Still - if you have one of the 99% of cars out there that CAN take an aftermarket deck - do it. It's as cheap or cheaper than a good line level converting system.

 

Everyone is giving good advice, but you need to know what you expect to get from the system. An oem/aftermarket system can work well if the oem set up is decent to start with. I had a 1995 mustang with a mach 460 sound system (jbl speakers, 230 watts rms oem) that was decent, but i wanted more bass and brighter highs. I added subwoofers, amp, loc, and tweeters to the factory system and it was very satisfying until i sold the car. All depends on what you expect to get and what you have to work with.