to power regulate the Shark, You "only" have to dissolder the small poti, then wire
a) a large external one to the contacts, or
b) built a few (three) "power levels" with resistors that equal three settings of the poti
imho the b) is better, because the levels are fixed. With the poti one would always run the circuit at much more power than thought. Runtimes can not be calculated good, then.
and 2nd:
STOP!!!
what do You want to do?
ordered SHARK BUCK?
four of them?
MC-E wired in parallel?
what about "wiring the (parallel wired) MC-Es in Series?
I am not sure, if the Shark Buck works similar to the Shark, and thus if it grants the current is controlled, no matter how much led are wired in series. My guess were, that the Buck can drive a single parallel wired quad led, dunno of adding 2 additional led. If that is possible, You wont need another three of the drivers.
Anyone has surefire infos?
PS: that poti can be a normal one. It is a sense resistor, there wont be a 3 A current on it.
(which is good, because the 3 or 5 W poti You asked for are expensive, difficult to get, HUGE and get very hot)
PPS: the XP-Gs can "replace" parallel wired quad-led, but the full 3A current will kill them immediately. Their max safe will be some 800-1000 mA, like the single die led they are.