Hi pupil, You have to use a phono preamp to bring the signal up to line level when your using the RCA inputs on the LS50W. The owners manual states this as well. So, any phono pre amp will work. One of the phono pre amps you mention should work beautifully. Congrats on your purchase, these speakers require about 50-100 hours to break-in. How long have you had them? Also, I would highly consider a E series sub from JL Audio. (E110, E112) connects using a rca from your main LS50 speaker.
Matt M
Matt M