Upgrade from Martin Logan Sequel II's to ????????

They're a panel speaker, yup they're the bottleneck in your system but that is just my anti panel bias showing strongly. Hope you get to demo some stuff cos I know you're not buying off of recommends here.

Anyway look at this - SourcePoint 10 Bookshelf Speakers (Black, Pair) **OPEN BOX** - Music Direct

@chippieboy 

Look into the latest version of ATC SCM40 passive. Used within your budget. 
I owned ML Aries and Montis and heard the Sequel and SLIIII. They’re old. The SCM40 will have similar delicate and warm sound but will be more resolving and easier to drive. A much more modern sound. Audition them if possible. 

kofibaffour, can you please explain in a bit more detail what you meant by "I know you're not buying off of recommends here."

What improvements and sound characteristics are you looking for?

I do not believe the Logan’s are your weakest link.  I believe the weakest link is the internal MAC DAC and use of a PC for streaming.  I recommend a dedicated DAC  and streamer.   There are many choices each with their own sound pallet.  Go with preowned units.  For example, a preowned Bticasti M3 and Aurender N150 will get you in or slightly over budget based on HifiShark recent sales.  
 

if you are set on speakers, +1 @soix .   Define what improvements you wish to achieve over the current SQ of your system.  Once you have a goal, there may be options to reaching your goal other than disowning the Logans.  

@jsalerno277 +1. IMHO your streamer, DAC, and phono pre could all be significantly upgraded. 

Since you like panels, look at these

https://www.audiogon.com/listings/lisbecib-martin-logan-montis-floorstanding-speakers-dark-che-77931-full-range

Although they're a couple generations old now, a step ahead comparing your ML's

Still relavant and better mids/highs than many current $10K speakers?

Long game-If you're a real LP fan, separate phono and upgrade from the AT OC9 to ART9(big upgrade for not much $)

The LFT-8B should fit the bill!

https://www.eminent-tech.com/main.html

Moving from panel speaker to box, prepare to have your soundstage shrunken in width and depth, you image specificity to suffer, your transparency to grow veils, and male (and some female) vocalists to sound chesty and boxy.  I estimate 2 weeks before you start regretting your decision to move on.

Thanks audphile1, There is a Dealer 10 min off of my commute in Saratoga. I will set something up.

soix, I'm not sure what exactly I am looking for sound wise. Something is missing.

jsalerno277, I agree on the DAC and the way I stream. Still not that happy with vinyl as well. If and when I do a speaker upgrade, the DAC and Phono Pre will be next.

tablejockey I not really sure I am a panel fan. I stumbled across them and wanted to give them a try. I will look into the ART 9. That was on the roster last year.

yogiboy as for the speakers you recommended, there is a dealer in Sacramento down the street where I used to live. I will set something up with him soon. I know the place.

jhnnrrs, I was thinking the same thing. I like the way Julie London's voice sounds on the panels. The Liberty Label Recordings sounded pretty good. If you are a Boomer or Gen X'er you should read the story of the Executives at Liberty. Pretty good story. Other Generations will not understand.

Thanks everyone for the great ideas. Please keep them coming.

I think you’re going to like ATC. One other speaker that I can think of that does the mids really well but needs careful matching is B&W. May be the older 804D3 is within your budget. They do love high quality power though. Don’t listen to all the B&W haters out there. Check them out. Easy to audition the newest series in best buy. Nay be even listen to 703 S2.