Where do I go from here?

The audio quality I have right now is the best I have ever had in my life, and I am loving it!  Full stop.  Work on the room. Don’t change the system. 

You are off to a good start! I used to have Heresies from the 80’s, great speaker for that period of my listening, but definitely due for an upgrade. Start with speakers, take your time and find a brand/sound you like. I would not get hooked on B&W, nothing against the brand, but there are a lot of good choices. While not the best place to audition speakers and gear, I highly recommend attending a show to hear a lot of different systems. I attended AXPONA last year for this purpose and it was very helpful. 

The audio quality I have right now is the best I have ever had in my life, and I am loving it!  Full stop.  Work on the room. Don’t change the system. 

This is absolutely right. Even if you do decide to upgrade equipment, the room is 50% of the sound. Get that right, first, and then do the other upgrades. 

Just for starters: you, like me, have very low ceilings. That has to be addressed. 

Imagine you're eating a meal and there's ketchup all over some of it. Someone says, "You should try a better cut of steak." You would normally reply, "Ok, but will that have ketchup all over it, too? Because I'm not buying more expensive steak unless I know I can taste and appreciate it." It's the same thing, possibly, with your current room. Learn how to analyze it and be willing to experiment until it sounds good. Then go spend on gear.

A lot can be done with speaker placement and listening chair placement to improve sound such that room treatment need not be extensive and ugly.  What you should do may depend on any restrictions you have on such placement.  For example, if you are forced into a placement near the side walls, treatment of those walls may take more priority.  If you are going to be seated relatively close to the speakers, much of what you hear will be coming directly from your speakers and reflections off the walls, ceiling and floor become less of an issue.  Consider speaker choice in conjunction with you placement requirements.  For example, if the speakers must go in the corners, look for ones that work well there (e.g., Audio Note).

You should take advantage of the help the treatment product firms offer in planning your treatment.  Whatever they say, start slow and do your treatment in relatively small increments so you don’t overdue things and end up with a dead room.  I would start with non-treatments that are practical and decorative.  Bookshelves that you might need to hold books, records, whatever, do a good job of breaking up reflections off the wall.  Decorative tapestries do the same.  Artificial plants (this is a basement), such as ficus trees do a good job as room treatments.

There are way too many possibilities for speaker choices so I will limit my suggestion to mentioning Volti speakers; if you like the Heresy, you will probably like the Volti offerings and they are a substantial upgrade to that sound.

Speakers typically have the most influence on what you hear, as they're the interface for the room.  The room is there to stay, but acoustical treatment can have a significant impact, so is a good place to spend some research time, and experiment.  

Speakers are extremely personal (and room dependent), so I won't advise on specifics, but get something you love the sound of and that works well in your room, then use an amp or amps that are up to the task of driving them.  A good dealer will let you try them in your room, and some online places have good return policies.  Used is often a good way to get the most for your money if the right deal comes along, but home trials are more difficult with used, however there's typically less financial loss if you resell.  A good kit is another way to get superior performance per dollar spent, but resale is typically more difficult, as is in-home trial...great way to learn a lot. 

Another option is to update the crossovers in your Heresies.  Crite and others offer upgrades.