Front to back... source to speakers.
Great speakers can not make up for any lack or loss of signal info which occurs due to source errors or degredation along the transmission pathways. ... they may reveal these errors though.
I became a 'true believerr' in the "It's what is up front that counts" camp quite by accident. Later, by practice. I auditioned a pair of $7K Speakers incorporating a good preamp, source, and my Krell amp. Even used front to back Audience cables and Chang pc. Nice. Nothing to jump up and down about but pretty nice. I declined to buy the speakers following the preview, intimating that the sound I heard did not correlate to the price I'd have to pay for that 'sound'.
I was taken into another room... A whole different setup for the most part, same cables and pc, and half as expensive speakers... $3.5K.... and 220 wpc less. it was comprised of the top Shanlin SACD/CD player, tube preamp and tube monos. Dollarwise, that front end was well over double the previous one, and the sound was stunning. Vastly superior. No question about it.
Following that eye & ear opening experience I bought an updated version of the same preamp, and have improved IMHO on the source, parraleled the monos and improved upon the speakers, cabling, and conditioning. Every source change out has again elevated performance of the system on the whole.
I've got 5 pair of speakers on hand, ranging from a few hundred dollars to over six grand per pair, a few amps, and various cables... regardless the spekers being used with my gear, the better the source, pre, and amp, the better the sound. Period.
That being said, the amp + speaker match becomes more and more integral as your system escalates... and/or the speakers own impedance curves stray from lineiarity.