Modern "Vintage" Sounding Preamps

     Purchase most any tube preamp, and load it with NOS, British valves (Mullard, Brimar, Genelex/Gold Lion, etc), to get that vintage warmth.

     If that doesn't sufficiently warm your heart: replace the signal path resistors, with Carbon comps, starting at the inputs, until you're happy.

     Some Paper-In-Oil caps exhibit a cozy signature, as well, in the signal path (ie: to warm up a later model CJ pre, replace any white or yellow (Mylar), plastic wrapped caps).

     I had a few customers, that enjoyed that flavor and: "The customer always thinks they're right!"

     I was in business, to satisfy whatever palate walked in the door.

    Some ideas (soundwise), were you to find a nice 6SN7 pre, per tubes to choose:

                              http://www.audiotubes.com/6sn7.htm

     The nine-pin miniatures, from those companies, have the same attributes in my experience.

      If you want less warmth, with the minis: Those from around Holland, Belgium, etc, (ie: Amperex, Bugle Boy, Philips, etc) may suit you best.

     There's a ton of fun to be had, if you take up tube rolling.

     Even more, if you can (or learn to) solder.

     If you do go tube: before you purchase tubes, be certain they are tested and certified to be, as absolutely as possible, QUIET.

@musicfan2349 -

     Thought I was being pretty clear, but: the SP-11's signal path contains metalized, plastic film caps and wire-wound resistors, which (in my opinion) aren't, "vintage" parts.    It does have some older-tech components, in the mix, which (to me) does put it on the cusp of vintage/modern.

      No doubt: that pre could be warmed up quite a bit, with the right valves.  

      Basically, to me: the old Black Cat, paper/Mylar caps and Carbon comp resistors, in the signal path, were (largely) what gave the older gear (circa 60s/early 70s) the, "vintage" sound, some love so much. 

      The older ARC pieces had Black Cats, in their power supplies, which may have warmed them up, somewhat.

       I owned both SP-9 and SP-14 pres, which I greatly enjoyed.    Neither of which sounded like ARC's very early iterations.   Especially with the early 60's, grey shield, Siemens CCa in play (my 6DJ8 variant of choice).

        Still: from ARC's inception, the goal was to resurrect/reintroduce tube circuitry (transistors being the rage, then), with a cleaner presentation, than what was available with older tubed circuits (as I recall).

      Don't know how ancient you are, but; being 75 years old: I suppose my views are somewhat different than later generations, far as, "vintage".

                                 Like I said, "Just MY take:"

              It's not my agenda, to change anyone else's opinions!

                                      Happy listening!

@musicfan2349

     Just my take:

     Though my response was how to obtain the sound signature in general; the OP already owns a CJ PF-1, loaded with wire-wound resistors and metalized plastic film capacitors, as is your SP11 (NOT a, "vintage" (though an excellent), piece of equipment).

     The presentation they’re looking for can easily be attained; through a few simple, internal mods, or possibly: valve changes.

                              No further equipment purchase necessary.

     I agree: there are numerous older components, well worthy of resurrection and updating.    I've done a lot of that, over the decades, though typically: to obtain less coloration.

                             Again: up the to owner/customer's tastes.

"My point, is why buy a new preamp/design when you’re looking for older sound?"