The hiflow muffler could be any brand. Chances are it's a straight through 2.5" muffler which will help immensely. Lukey is a good brand, but I believe most to be fine really. There is a thread on Street Commodorees about exhausts which is very informative and worth a look. It explains there are 3 basic types of mufflers. Straight through offers greatest performance gains, while people believe the lukey triflow (turbo style mandrel bent muffler which reverses the gas flow several times like your original) or the dogleg (has a straight through, but the internal pipe has a slight kink) produce a nicer note.
Now about your resonator (long round muffler at the rear of the exhaust) is there one there, if so is it original? If there is not one there, I would consider it an idea to have one fitted if the sound is 'droney'. If it is original, I would consider changing it to an aftermarket 2.5" version.
The 'muffler' thing behind the extractors sounds like it is the cat (catalytic converter) which is fitted for environmental reasons. I prefer not to alter these, as the original (if in good condition) dont restrict flow much at all, and actually help the environment a great deal. One in poor condition will block exhaust gases causing loss of power, and increase fuel usage.