SEEKING ADVICE: Which component would you upgrade first?

Speakers speakers speakers x100! You have unlimited room for improvement with better speakers but you could buy $25000 worth of Mac or Krell and it’d sound a little better ,maybe. Second would be a dedicated phono stage followed by a good cartridge unless you have a good cartridge already 

@markley what are you missing? Obviously you can start with the speakers, but what are you expectations?

people are not paying attention

either to OP's budget (+/- a few hundo)

or his existing speakers, I looked them up

go to hifishark, check the prices asked for his Pioneer HPM-100 Speakers 

what the hell do you think would be better for a few hundro????

these speakers have Level Controls, giving the ability to adjust for both the space and OP's preference.

The receiver/tt/speakers certainly would reveal the improvement of a new cartridge, AND, the investment of a new cartridge can be moved to a new TT when ready.

Save money for quite a while before looking for better speakers

My suggestion is to start with cleaning up your power. Once you do that everything down stream will take on a life! However you will need more than a few hundred to do it right.

The HPM-100's were designed by an engineer Pioneer hired from JBL and were their answer to the 1970.s JBL L-100. Nice speaker in its day but IMNSHO, the absurd prices those speakers are bringing today is tied to the vintage-gear rage. Speaker design technology and philosophy have progressed greatly since the HPM-100's were built. A wise hi-fi mentor once told me, "if you want to make the biggest change in the sound of your system, get different speakers." I agree witih him. And if it were my decision, I'd sell the HPM-100's and take the money from them and look into some Vandersteens, Monitor Audio or Sonus Faber.