best sub and amp?

The type R is actually a pretty darn good sub.  But as in ANY audio gear, you have to like how it sounds.  If what you're seeking is more SQ (sound quality) then here are a few suggestions.  1: stay with a sealed enclosure always for highest SQ.  Make sure the enclosure is completely sealed (all seams and woofer mounting area are air tight.) Make sure it is the correct size for the speaker.  2: stick with a good mono sub amp like your MRD 500.  In fact, this is a great amp and you should stick with it.  3: If you have tried the Type R in a proper sealed enclosure and have the amp set up correctly and you did not like the SQ, before you buy new gear try moving the sub to diffrerent locations in the vehicle.  If it's in the trunk, try facing it forwards, then backwards or to the side.  Try firing it towards the cabin and then flip it around so it fires towards the rear.  Try moving it around to the front of the trunk and then to the back.  Spend enough time at each location to listen and evaluate any difference.  4: The MRD 500 amp includes some very sophisticated digital electronics for time alignment and EQ.  Read the owner's manual carefully and try adjusting the settings.  You may simply be hearing acoustic phase cancellation or improper EQ and need to correct for it.  5: If you remain unhappy with the sound of the Alpine, the next steps up in quality include speakers from companies like Eclipse, JBL, Nakamichi, Diamond, Dynaudio, Morel, MB Quart, some of the drivers from Planet Audio, Adire and Orion, and if you really want esoteric try to find a Magnat.  Realize that (depending on which one you have) the Type R retails for less than $200.  To step up in quality to the level I am suggesting will require about two to five times that much and more.

Good luck!

You might try listening to an Eclipse aluminum 10" sub. You could use the 4 ohm dvc version with your alpine MRD-M500 amp and it get 500 watts (which is the reccomended rms power). They sound reall really good in small sealed enclosures, and retail for around $350 in the U.S.

In my opinion the best all around sub on the market today (meaning sounds really good and can generate prodigious SPL) is the JBL GTi series.  Take a look and see if you can find a W12GTi.  I doubt you can find a Magnat in the states, as they are not directly imported here.  Now and then some of the more esoteric shops will have one that was brought in.  The Bulldog sells for around $1000 for the raw speaker.  I recomend you keep your Alpine amp if you like it.  It is a good amp.