Considering a POSSIBLE replacement for speakers. Opinions?

You'll need two subs for proper stereo reproduction.

It's very risky purchasing speakers without an audition. All the above recommendations are someone else's ears, components and room. The number one mistake folks make is purchasing the wrong speaker, especially speakers meant to be out from the front wall (most) which end up positioned incorrectly for whatever reason. Then they try to change the character of the speaker with electronics, wire, etc., a hopeless cycle. Great for dealers though.

I've heard several of the recommendations above set up fairly well with good to very good upstream components with very disappointing results.

You may find this book, Get Better Sound, useful.

https://www.getbettersound.com/

There are audio shows coming up. I plan on attending the Capitol Audio Show this year. Keep in mind that the rooms are generally horrible BUT, you can get a sense of what appeals to you. I always like the sound of the Thiels at the shows. My thinking was " If they can sound decent at the show, they'll only improve at home". Lots of fun to meander around the rooms as well. Good luck. Joe

AXPONA in chicago is a go this fall! You could hear lots of speakers in 1-3 days time.
Moving up Monitor Audio’s lines is a great idea. IF you knew you liked something you could wait and watch the used classified advertisements.
You are definitely, as is noted above, in a tremendous sweet spot for sound and build quality at you budget.
One recommendation: Enjoy the process! I wish I was researching stuff in that range. So much fun!

As mschott astutely pointed out, this has a lot to do with your amplification source and other components in your chain. Actual critical listening sessions under controlled conditions is always best. However, I empathize completely with how much more difficult that is to do these days! As such, I would recommend you speak or communicate with as many trusted & knowledgeable audiophiles as possible to get a better perspective on what might appeal to you and work best in your home and with your components. These are some on-line sellers whose guidance I’ve found relatively trustworthy over the years: Music Direct; Crutchfield; Audio Advice; Audio Advisor; World Wide Stereo. Of course, all of them will try to steer you in the direction of the products they sell, which is understandable.  All the more reason to speak or communicate with as may sources as possible to get a better perspective. You might also want to consider posting this question on other sites like Stereophile; Soundstage Hi-Fi; etc. Sometimes, you can even email professional reviewers for guidance, as well. Good Luck!

FWIW, Listing your system in your profile is helpful for just such occasions where recommendations are sought. Based on my experience, I think that high powered amps are not necessarily a good match for efficient speakers. But I don't know what amp you are using so its a shot in the dark to recommend anything like Tekton that is high efficiency speakers but have a large following. Stay with MA if you like the sound you have now, and want to keep that sound.