Unless you are the only one watching, I find that the centre speaker is the most important. It ties the speech to the centre of the TV. Off axis viewing is unnatural without it.?
The sub also is extremely important. Personally, depending on your budget I would go for smaller (and presumably cheaper) front speakers and include the sub.
You mention the Lektor 6 5.1 system. That uses Lektor 6 for fronts. I would swap to Lektor 2s, a Lektor LCR and a decent sub. You "could" go for the Dali sub, but you'll get better value from BK or SVS.
Then you set the fronts to "small" on the AV amp (something I prefer to do myself even with floorstanders - I was running a 3.1 system with Ikon 6 fronts, Ikon vokal 2 centre and sub and always preferred to let the sub do the grunt work).
IMO, unless you have serious money for huge front speakers then they can't keep up with the low bass in films. I found the Ikon 6s were fine with most (not all) music in this regard, but struggled with proper AV. Setting them to small and letting my sub do the work was much better.
However, saying all that, you may want to get the best you can now and save for later...in which case, go for the 3.0 with the floorstanders.
But there is nothing in an AV system quite so satisfying as when a sequence with proper, deep, rumbling bass starts to shake the room and you feel it in your guts!?
(You will not get that from a pair of £600 floorstanders)
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