Itching for better sound


Pretty happy with sound through my Sennheiser HD700s listening through headphone amp to classical CDs on Marantz CD6006...but too much headphone listening makes my ears buzz, so I want to start listening more through speakers.

Could set up either the Marantz or a NAD 516bee cd player, connected with RCA to an old Denon AVR1404 receiver to speakers.  My PSB speakers are fair.  What I want to know is how much will a pair of Kef LS50s improve my sound?  Is my $800cdn (used) better spent on something else--other speakers or another component?
shostakovich
Was that plywood/sledge for the famous "hammer blows" in Mahler 6?  I'll be attending Mahler 2020 festival at the Concertgebouw in May--NY, Berlin, Vienna Phil among others.  That should whip even the finest audiophile equipment, and it's why I can't afford any major upgrades just now.

Thanks to everyone for their input.  I will keep my ears out for the right amp!
As for the Rogue, I really need something to which I can connect two sets of speakers.  Is that an audiophile no-no?

Would welcome any thoughts on these three amps: Yamaha A-S801, Marantz 6006, Cambridge Audio CXA-81.
I would go for the Yamaha, it has the most power of the three and the lowest price. The Marantz seems a little under powered. The Cambridge does not have tone controls which may or may not be an issue for you. Of course the sound quality is the most important and I have only heard the Yamaha and it seems to be a pretty nice sounding amp.
My A-S801 really makes pianos sing - and the inbuilt DAC really pumps up the value/performance ratio. 
D'yall think my non-audiophile ears are going to hear a dramatic difference between my current Denon AVR1404 and the Yamaha A-S801?