An ideal (minimal) 2.1 setup

where's the center channel speaker?

Doesn't need a center channel, but needs a couple of subs.  If choice 1, a KEF KC62 would seem ideal -- Darko review.

I'm more interested in the distinct sound signature differences between the two.

To me, it's all about clarity and detail. You don't need a center channel, but do need a couple subs.

ET LFT-8s and really move up a big step. 

When you say movies do you want the loud theater type of sound? If so I think the kefs hight run out of steam even crossed at 80hz. Or at least struggle to keep up with the subs output at high levels. 
As for the Kef sound. The kefs have a very wide soundstage that still has good center focus and are very neutral. The down side of the kefs is they lack dynamics and the highs lack refinement to my ear. I have always passed on Kef when directly conspired to competitors of the same price. Tue LS50 might be the exception as they are pretty cheap for what you get. But at the Reference 1 level and up I would take different brands. Just my opinion. 

What amp/processor?  Or, are you just using the digital out from the tv?  Also, with only 2 channel it will make a difference regarding speaker placement.  You need the speakers tighter to the screen for movies but probably pulled out into the room for music?  just my concerns.
The sound on OLEDs is better than most tv's but still crummy.

If the program content has center channel info, and you have no center channel, then don't you have to downmix to forced 2 channel mode?

If you just don't hook a center channel up, the center channel signal is still NOT in the front L and front R.

I guess the movies are more casual than anything serious (not looking for theater loudness). More priority to music to I would place the speakers apart for music and not have a center as I'm trying to keep it as clean as possible. For the KEFs it would be out from TV since its an active. 

How about a NAD M10, some Revel M106s and a T/7x?  With eARC the audio will be automatically downmixed to 2 channel…no loss of information, and the speakers will give a solid central image without a dedicated channel. Dirac Live will tune the system response to your room below 500Hz. If you don’t love the M106s substitute another similar speaker. 

The size of the woofer matters a lot.  I've never found little bookshelf speakers satisfying for rock.  Little speakers + subs can have the same frequency response as large floorstanders, and can be comparable on some types of music, but nothing large scale.  If you listen to Beethoven or any full-bodied rock I think you'll be disappointed with little bookshelf speakers despite plenty of deep bass from a sub.  

A 77" image, movies, only 2 channel?

At least consider having HT Bypass feature for future options

We just thrashed out how to have an excellent ’FRONT’ 2 channel music system, like what you are planning,

and have an AVR for movies. AVR uses that high quality 2 channel system for the front and the AVR drives the ’other’ movie sound channels, i.e. 5.1 .. Center, rear surround L & rear surround R.

https://forum.audiogon.com/discussions/avr-internal-2-channel-audio-mode-or-ht-bypass-external-equip...

Bass: Subs: you will want ALL the BASS to be part of the FRONT 2 channel system, thus ALWAYS there via Large Mains, or a PAIR of subs front firing, no ports, adjacent to the smaller mains. Directivity, Imaging comes from the fundamentals and all of those fundamental's overtones, i.e. 40/80/160/320 ....

Go with the Kefs and a Rel sub (s).

I have a 4 K TV, is the OLED much better?

The QLED abs oled are pretty comparable unless you are a video nut. In a normal room the bright lee QLED will be better. In a dark room the oled pulls way with deeper colors and blacks. But in a dark room you should movie to a projector for the real movie experience imo.
Anyway you should listen to the kefs. They get universals praise but I don’t find them every involving or particularly good. They really lack dynamics to me. Subs will not really fix that. Again a lot of people love them. Just depends on what you are used to. The active kefs might be better at dynamics.
For casual movies any of these speakers will be fine. For legit home theater bigger the better. Phantom center is better IMO and even in my detonates media room I use phantom center.

Hello,
I’m thinking the KEF LS50 Meta and the BlueSound POWERNODE along with the KEF KF92 Subwoofer. It’s the big brother to the KC62. The POWERNODE  has an optical input for the TV. You can stream everything to it. The KEF KF92 does not have to be placed in the front in between the LS50 Meta’s. The KEF KF92 has 50% more volume than its little brother but has all of its capabilities including an optional wireless kit for $200. This will let you put the sub where it needs to be vs where it has to be. The BlueSound POWERNODE lets you blend the sub to the front speakers right from the BLUESOUND app. This package will be $4600 plus speaker wire. Or you can go with the wireless LS50’s ( still has the META plate) and a BlueSound NODE with the KEF KF92 sub for $750 more. There is a KEF app for the KEFs and more connections but I prefer the BlueSound app. I hope this helps. I am in the same boat so this is what I came up with. The store that is a KEF dealer near me lets you try this out before you buy. https://holmaudio.com/Also, this store is selling the Node 2i for $449. This will put you at $650 more if you pick the previous 2i model. These powered LS50 wireless were John Darkos top pick at this price. You cannot beat this value. 

Seems like a lot of KEF fans. Any reason why Spendor's are not a better match? Atheistically love the look of them as well.

OK,  your focus is music and you seem not interested in the deepest bass for movies. I get it I used my system the same way. Stand mount monitors, no center channel or subs. Wonderful holography with both movies and music. If I had a sub I would not use it for music.  I am on the side of going with the speaker that most pleases you when in music mode.

One thing you may want to think about.

My stereo does double duty for music (mostly) but also sees heavy use when watching movies and also regular television programming, via my cable box, which can have great soundtracks.

I strongly prefer the silk dome tweeter for music, but sometimes think I may prefer a metal dome tweeter for dialogue. 

I have owned many Spendors. I doubt that you would go wrong with the A4! If you want to go with a standmount and a sub the A1 would be another consideration!

Sorry I can't offer an educated opinion on the two options you have, but my apologies that so many respondents want to address issues other than yours.  It's a simple question.  I use my audio gear like you do and use it  2.1 for movies.  No problem with dialogue/center channel. 

Thanks, I think the last few posts got my dilemma! I don't care much for bass. I'll go with Spendors then.

You sure won’t regret that decision!

Any chance you can audition both speakers? Each is widely distributed, the Kef more so. 

These are speakers different in design and in performance. Further, the Kef offers a significantly different feature set. The cost differential is significant as well (based on your figures).

There is a lot to consider and balance. 

Bass is foundational and key for both music and movies. I realize you've stated that you " don't care much for bass" but I encourage you to care as I believe you will be rewarded for both your music listening and with movie soundtracks.

FYI, I run a 2ch system sans subs, with an approximate 80:20 music:movie mix. TV is a 75 inch screen.

Knowing your room size and room constraints will help tremendously. As will lifestyle and aesthetic considerations. 

Try the vintage jbl l212 system, or at least try to hear one. You will have to go out of your way to hear one but you will be pleasantly surprised when you do for sure.