Welcome to the forum. I wish I could help you but I have no experience with the gear you mentioned. I'm sure someone here does.

for sure. Probably one of the best budget loudspeakers out there. But I'm not quite sure why you got the center channel SP-C21 which would be great for a home theater but not necessary for a two channel music system. Looks like now you need a good two-channel integrated amplifier. NAD, Music Hall, Cambridge Audio come to mind. Or sometimes one can find $300 deals on the Harman Kardon HK3490 stereo receiver. Looks like its $305 at Amazon right now and $300 at J&R.

The HK3490 has a phono input, so you would be good to go once you get your turntable. New, a bare minimum in my estimation is the Music Hall MMF-2.2 for $450. Or lots of used options.

the Harman Kardon HK3490 from J&R for $300. Better act fast as the prices for those units fluctuate from under $300 to $450.