Hand me down audio equip- upgrade advice

Nice gift from "da boss"!  I would suspect he or she is a valuable resource as they owned the equipment and upgraded the whole system.  Maybe you can follow that same road to a lesser degree. Get the room straightened out, that will pay you back with any system you acquire.
Good luck, go slow.

Lots of good advice above.  $1500 doesn't get you in the game these days unless you get lucky, or can fine another mystery benefactor!  I remember the 103/3 w/KUBE without a lot of fondness, so the upside is large if you are willing to re-foam another used pair of classics...find a good pair of Theils, Snells, or a/d/s L1290s if you can, or SF Grand Pianos.  Also, if you are handy with woodworking tools, consider a pair of Dayton Audio Solstice from Parts Express...all Morel drivers.

Thank you all for your comments and suggestions! To answer @three_easy_payments and some others- I don't have any acoustic treatments currently- I'm actually planning on moving in the not too distant future... so much more effort will be put into the room after that happens. 

I didn't know a ton about higher end audio equipment until after I received this equipment as a gift, and after doing a lot of research- I'm very blessed and thankful indeed! 

@barts I have been working with him on plans for an upgrade, but he is currently very far out of my league on everything... He has given me some solid tips and advice though. 

@audite84 and @crustycoot Did you personally refurbish your 103/3's? or did you have someone else do the work? I refoamed the woofers in both speakers, but haven't touched the ferrofluid in the tweeters yet. I've been debating whether or not to do it myself or have a shop do it. I know from what I've read that the tweeters are probably less than ideal as they sit- but I have to say I'm still not convinced they sound bad by any means. I've also had my eye out for older Theils and SF varieties, and will continue to look. I'd love finding an older pair that's not too beat up that I could refurbish.

@guy-incognito I've been having the same inclinations you mentioned, I'll probably just continue to hold out until I feel comfortable spending $5-8k and in the meantime keep an eye out for deals of older proven speakers that I might be able to bring back to life. 

@millercarbon and @soix I see what you’re getting at, part of my issue is definitely the lack of auditioning. I think what I’m after is a more full range sound. The KEF’s really struggle with mid-lower range (I have done different tests on them, but don’t remember the exact roll off struggles). I primarily listen to a lot of jazz, symphonies, 60’s and 70’s light rock, with some hip hop thrown in there occasionally. I’ve been keeping my eye out for a second vandersteen v2w that I could incorporate into the system, but ultimately would like to get a bigger sound stage than my current KEF’s.

Explore planars perhaps—Magnepan/ML.. you don’t pay for expensive boxes ie.good value/sound for the dollar—life-size staging and sounds great generally—should work well with your current rig.