The PAC Pro Reference II is very similar to Audio Research SP6B! The regulated power supply used servo op-amp with same transistor as ARC SP6B ( MJ423/413 and MJ4361). Phono stage is similar to Marantz 7 (SP6B too) , parallel cathode follower, hence 8 12AX7 tubes (ARC used 6). PAC Pro used independent tube per channel, ARC shared the dual triode between channel, but if you have T adapter in SP6B (become 12 12AX7) then it will used idependent tube per channel. ARC SP6 is better built.