i bought some MB Quart DSE216 and DSE169's today. pair of each, hope their good, they sounded better then the Pioneer Pro's that they had there at 300 for the 6's and 400 for the 6x9's.

I have MB Quart splits in the front of my TH the sound is great, very crisp and clear, I'm very happy with them

I have the same speakers (front splits)
just well maybe.. ok.. i only have one front tweeter cause one got hacked to bits... oh well... but it sounds good.. better than the 6x9's at the back (pioneer 200 watt 3 ways)

I have the 6x9's You mentioned. excellent speaker but your definately going to need to get an amp for all of them... otherwise you do them no justice. I shall be getting some of the RCE216 splits for the fron hopefully soon. With the speakers if you werent told, you need to run them in for about a week or so. They get better after then.

YES get an amp, you will notice a difference, I have a Pioneer 9450 and though its 50 x 4 I got an Amp which was 60 x 4, and what a big difference it made to the sound, if you spend the money on the speakers, the sound quality will fo up a fair bit over stock but get an Amp and it's 100 % better again.

he tells you no lie! Aside from the fact that they will sound 100% better, you will have much better control over your speakers. You can change the gains, the high pass/low pass frequencies PER channel, which basically mean you can decide how much bass goes into each speaker.
If you can afford an external amp, DEFINATELY invest!

i have a set of rsd216 or what ever they are... not a bad speaker... but no way near worth the amoun tof money they retail for... lucky i got them brand new for $200
at the moment they are in the back parcel shelf..
mbquart tweeters are too sharp and loud on the ear especially when a decent amount of power and voluem are going through them.
and the actual woofer can play very much mid bass att high volumes... they just clip
also the mbquart woofers are a very nasty sounding woofer... if u have them installed cover or disconnect the tweeters they dont sound very nice at all...
i was runing trhgouh a pioneer 7350, through a active crossover and through a v12 alphine amp and they didnt impress me all that much...
i got my hands on a set of hertz when i was over in thailand and they absolutely p*ss on the mbquartz. they play louder, more bass, clearer cleaner and very happy with them... the price u paying for the mb i qould reccomend having a list to the infinity kappas they a little cheaper but sound alot nicer........ audiocom stock these