Sounds like a plan. I skipped on LG SL6Y bar because of bad reviews when I bought my C9, and later, when Rtings tested it, it was confirmed that its response is terrible. Do listen to it though. Make up your own mind.
Take some songs that you know well. If you have some good headphones, listen to the selected songs on them a lot so you know what to hear.
JBL has a bar, 5.1 Multibeam, which uses side firing tweeters and room correction for that too to create a wide soundfield. It needs walls within 4.5m of each side to bounce sound though. So I'm not sure how it will sound in an open showroom floor. Still, check it out. It'll fetch you a 10" subwoofer too. Doesn't have a lot of settings though. Getting good reviews on Bestbuy currently. No option to add rear speakers, which you can though with LG and Samsung options. Don't think Sony has any bar in your budget that you should consider. They tend to lack treble anyway and sound dark and muffled.
For Atmos requirement, there is a new offering from JBL, the JBL 9.1 (5.1.4, basically)