Seriously, forget about that "Heartthrob" junk from JC Whitney. I looked at the link. It's just a cheap "universal" kit that universally doesn't really fit anything. It looks like it's meant to dump 1 pipe on each side, in front of the rear tires. That definitely won't work on an explorer! As for Cherry Bombs, you may get the sound you want for a short time, but 1.) the fiberglass packing will eventually blow out, 2.) the shape and size of the typical cherry bomb will make fitting them under an explorer a challenge, and 3.) cherry bomb style mufflers, with fiberglass packing, are not the best flowing mufflers. a well designed directed flow muffler is much better, as well as not having any fiberglass packing to rot or blow out.
Also, believe it or not, a bad exhaust (too big or just poorly designed) will actually lose power. Single IN and Dual OUT will not help you. It will just be a headache, as far as routing the pipes.
As I said orginally, try talking with James. But, I believe your best option is either the Gibson, for power w/ mild sound increase, or the MAC cat-back, if you just want it louder. I was told that power was about the same for both. If anything, the Gibson makes a little more torque in the mid-range, which is what our heavy beasts need; whereas the MAC may give up a little torque for a few more HP up top.
Another option is flowmasters, like Al said. However, in doing some research on this for myself, I noticed that a lot of guys who went with the 40 series, or the Delta Flows found them very loud and a bit "buzzy", which is something I want to avoid. Perhaps the 70series, as Aldive suggested, is different.
If you have a local shop that will work with you and isn't expensive, than you could go that way, otherwise, I think the gibson is probably the most cost effective option, as it does include everything needed to just bolt-up to your stock setup.
Now, as for the Cold Air Kit, that might be something you could "skimp" on and make yourself. Granted, it might not be flow tested like a commercial kit, but it would be better than the stock corrugated hose and airbox. You could get an off-brand k&N style oval filter for $15-$25, and make the intake pipe with pvc pipe form Home Depot. Wrap it in aluminized foil insulation tape, for heating ducts, to further reduce engine bay heat from reaching your intake air. Just be careful to support the pipe w/ a braket of some sort to keep it off the alternator and the cooling fan. I did something similar on a 98 Cavalier 2.2L I had not too long ago. It was a lot louder when you revved it, but itimmediately picked up noticeable power and 3mpg! Man I wish I hadn't sold that car!-almost 35mpg around town-w/ a lead foot
