Why are the vocals on some records hidden behind the music on my system?

Help! I am new to this forum, but have been into audio for over 45 years and have never had this problem before. I was lucky enough to come into some money and decided to use some of it to up grade my system for the first time in almost 30 yrs. The system consists of McIntosh MC-402, McIntosh C-100, McIntosh MCD-500, VPI HW19 MKIII, Soundsmith Aida, Furutech Ag-12 phono cable, Furutech silver head shell wires, Furutech interconnects and Furutech speaker cables (yes I like Furutech) and Raidho XT-3 speakers. Now on some albums the vocals are buried behind the music and you have a really hard time hearing the singer? Not all albums are voiced in this manner but enough that it is bothersome. I have a large dedicated man room (24 x 27) with minimum treatment. CDs sound just fine so I feel that it is with the phono preamp in the C-100? I have moved the speakers 100s of times and have them at 5' 8" apart and 8' 1" to the focal point and the soundstage is good and the vocals are better, but you still have to really listen hard to hear certain vocals on some albums. Most of my albums are 30 to 50 years old and have been cleaned with a sonic cleaner (best thing ever imho). Even some of my new heavy vinyl has this problem.