@Audiophile, Nice configuration.
Regarding the pricing part, Hertz EBX 300 is really good in terms of enclosure design. But, I must say, once can choose a good sealed enclosure and use Hertz sub and get good bass too. While choosing custom/local enclosures, I prefer sealed enclosures. They perform better as its not complex to build them compared to vented or bandpass ones.
So, thats one alternative to factory enclosure and saves quite a bit of cost. Say, Polk Audio DB 1240 (SVC) in a 1.25 cu. ft. sealed enclosure will come in 9K.
I would prefer 4-ch + 1-mono, if you are not tight on budget. Orelse, you can simply use a single 4-ch amp and power fronts & sub, running the rears from HU directly ("Rear-fills scenario", which has been liked by many enthusiasts). Remember, for sub woofers, nothing can perform better than a mono!
Damping !! Difficult question.
Dynamat is too costly. There's one mat from DLS, that cost nearly Rs. 500-550/sq.ft.; It is asphalt based and requires heating while applying.
In Bangalore, we do use yet another local mat and our customers have reported that it performs better than NoiseKill (another mat in the market). It costs 350/sq.ft.
Look for mats made in butyl rubber and bitumen layer stuffing. They are usually "peel and stick" type and are quite effective and almost comparable to asphalt based ones, but with less health hazards!
I am not from Mumbai
