ppi art series ax 606.2

running  the 4 ohm dvc sub in parallel will give you 2 ohm mono load off of subwoofer channel of amp.  shouldn't be a problem.  you can always test the speaker wire leads coming off the box using an ohm/ multimeter-preferably digital.  this will give you an actual reading of ohms.  not a bad idea before turning on the juice, to make sure all wiring is correct.  some speakers actually run at a slightly different impedence than advertised-  usually not a problem. (example-12"pioneer spl3002 dvc 4 ohm subs:actually sit at 3.6ohms per coil) 

as for the front channel question;  i am not particuliarly experienced with this amp.  i will leave that up to someone else who is to answer.  (I would probably test the leads for actual impedance, and based on the results-make an educated guess as to if it seems ok to do.) i don't want to give you bad info-wait for another opinion before trying.    hopefully i was helpful.

ok- so, if you are going to bi-amp the ba's;  the ba crossovers will take care of the high pass filter that is necessary to protect the tweeters, as well as the low pass filter that is necessary for the mids.  the only thing left would be to set a high pass filter on the mids (probably use the one on the amp or head unit-around 80hz or so. i usually set according to how it sounds and how the speakers respond.  too low of a filter will send too much bass to mids, making them distort/possibly damaging them: too high of a filter will cause you to lose some notes and sacrifice the sound that you hear)  the only thing left would be to set that filter on the mids, maybe not a bad idea to set the same filter on the tweeters also- but it shouldn't make any difference, like i said, the ba x-overs should take care of it.  i would set them both the same, even if you hear no difference.  and using a bi-amp setup, you can adjust the gain controls of the front/rear of the amp to control the desired loudness of the tweets and the mids.  

rear fill?   well, i have always stacked up multiple pairs of rears and just ran one pair of fronts. (i always use overkill as a standard-lol)  this time, i am running three pairs if front separates, and only two pairs of coax's for rear fill.  i like this imaging better-more capturing, rather than just "blown away loud".      rear fill does help -a lot.   but, i don't feel it is as important as the front.  pretty much anything will help.  you can spend a lot of money, but you don't have to.  even just a pair of decent coaxials will greatly add to your imaging.  even if they don't see the same wattage as the fronts, or if they aren't as big in size as the fronts. anything will help.  ex- my sisters boyfriend has a pair of sep's up front off of an amp (chevy truck), and i threw a pair of 4x6" plates in his rear doors, running off the amp in his head unit-  sounds great.  not as loud as fronts, but enough for fill.    a lot of choices, all of them are what YOU prefer.  (i like having 32 speakers with 7000watts going to them in my extended cab pickup-no room for a family-lol!)

hopefully this is helpful- ask on if anything else.    and. YES, does sound like a fun family vehicle(lol) .  nothing wrong with looking good with the family.    

subs?  well, i have been kindof stuck in one corner on that end of the market. for the past 5 years i have run strickly pioneer premier subs.  i had four of the old ones with the 5 diamonds on the cone (model?). then i had two of the yellow spl ones.  then i had 2,12 inch-tsw-spl 3002/ and 2-10 inch spl-2504's, all running together in one custom box; the 12's running low pass at about 55 hz, and the 10's running bandpass at 55hz to about 100 hz,  they made for a real  concert sound.  now, i run 4-boston acoustic 12"g-5 subwoofers, with 4 boston acoustic 12"gtr radiators (passive subs) in the same box.  it sounds awesome! tight, hard, loud, and low-sub frequencies!     they also make them in 10 inch sizes too.  very small enclosure sizes (1.0 cu. ft for 12's, .5 cu. ft for 10's) and you can just add a passive to the same box without losing power handling-just sounds like you added another 1/2 of a sub)  the only drawback is the large magnets on the speaker.  and, if you blow them up, you can buy replacement parts to completely rebuild the sub for about 100 bucks.   if mounting depth is an issue.  if so, you should check out the pioneer premier sd(?) series subs.  they are made in tens, and 12's, require a small enclosure, and have somewhere around 3 and 1/2 inch mounting depth.  i put two twelves in an s-10 standad cab pickup! they aren't spl type subs, but do handle 1400 watts, and have a very deep, pleasing sound.   

jls are nice, too.  just haven't had too much personal experience with them.