Which to Upgrade first? My Amplifier or Speakers?

A pair of REL top notch subs will upgrade your low end and also your midrange/soundstage
and especially with the Maggies, plus you will have some cash left over, object here is to allow the maggies you love sound that much better!!!!

....just wandering by...

I’ll vote with @erik_squires ....but one can be subtle about it. Dipoles like Maggie’s deserve that...;)

Adding a sub could also be an easy +...but MHO, you ought to be able to ’do’ a better ’sub-weight’ than a barbell weight. (Unless you already ’do' weight training...*shrug*)  A nicely wrought box, matching the top dimensions of the unit as well as the finish would have a nice esthetic. Fill it with as much lead shot as desired...

You might look into active eq...that in itself can accomplish amazing results without having to get ’heavy handed’ about it, either.

If you love what you’re running now, minor tweaks vs. major moves seems more the way to go....beats ’buyer’s remorse’, too.

We all read about That a lot around here...probably more than we should. ;)

...as for interconnects, power cables, all that....

Read the existing forums first before pulling That trigger....
See what's already getting attached to Maggie's and Mac's already and place your bet thereby....

(Copy someone else's homework...*L*  Nice, old tradition, that.)

Norman, honestly, what do you listen to? Speakers or associated equipment upstream?
Get your speakers straight, then all of your sources (most of which are todays technology) will fall into place.

OK question for OP. You posted this on the pro section so are you interested in a rehash of all the homeowner stuff talked about so far or are you really interested in pro gear?
  Pro gear opens your world to astounding speakers from Klipsch. The K-402 horn lens is the best in the world right now and you can mate it with various bass bins either direct radiator or horn type.
  Currently I run a home build Super MWM bass bin which is a variant of the Klipsch MWM bin except mine goes down to 27hz as a single fold horn. On top is a K-402 horn with the 1132 driver and run it off a pair of Crown xli800's and a Xilica DSP. You can build an astounding system like this for about $6,000 and that is with new K-402 horns as your chance of finding used is about zero.
  If you are not into building but would rather just buy, the Klipsch Jubilee is a whole lot cheaper than a ton of all this name dropper stuff and has prodigious sound. If you really want to enter into the world of genuine hi end sound you are going to have to migrate to a DSP and multiple amps. It is daunting to start off doing this but the reward is jaw dropping sound and FAR less $$$$ than most all this fru fru stuff touted around here. You can PM me if interested and I will fill you in on what I did and why.
  Just for grins though you can look up Klipsch KPT-456, MCM 1900's which were my two prior systems and I can tell you the existing Super MWM beats the MCM 1900 easily. You just have no idea the superb fidelity pro gear brings to the table and a darned sight less than all that name dropper stuff.