I wouldn't rush into anything. See how the S5.5 sounds off the Accuphase. It may totally meet or exceed your expectations. I have two 45 yr old preamps that still sound great (to me), a Mac C27 (SS) and an ARC SP-8 (8 tube pre). I also do have a Coda CSiB V1 integrated; the preamp stage is some hybrid of a CB and 07x. My favorite of all is the SP-8. The CSiB preamp section is excellent though and very comparable to the SP-8 performance using either to drive a Mac MC2125 amp. I wouldn't sell the SP-8 or CSiB for a 07x to drive a S5.5, being very satisfied with the CSiB sound, quality, design, features. I am expecting the preamp section of it (similar to CB) to work fine with the S5.5. TBD. The SP-8 synergy is questionable. I definitely like good tube based preamps though so if buying separates, I myself would look in that direction, but get good guidance on synergy. The best way is trial testing in one's room if possible.
There have been some posts in this thread on Aric Audio Motherlode tube preamps that Terry London speaks highly of. Pricing is in between the CB and 07x. If your Accuphase sounds great to you though, that synergy may beat other separates so why gamble? If you are not satisfied with The Accuphase preamp section though, patience and careful research will pay off. You have numerous choices for your preferred budget. Ask Terry @johnah5 .