You could try a full function preamplifer with a phono stage (using the CAV-50 as a basic power amp, as none of the controls would be in circuit/functioning) but... all you need @ this point is a stand alone phono preamplifer to run through one of the Aux inputs of the CAV-50.
Posting a budget/price range will help as there are many to choose from.
If it's still for sale the Bel Canto Phono 1, listed in the A'Gon ads, would be a super choice, IMO, as I would use it myself having listened to one years ago.
The C-J unit mentioned would work as well as it's lowest gain is 40dB (or a bit more perhaps) for MM cartridges.
If you like the sound of the CJ with CD source I'll suggest you go with a basic "stand alone" phono preamplifier as to simplify your choices.
Adding a full function (including a phono stage) preamp to the equation kind of defeats the intention of owning an integrated amplifier.
Hopefully someone else will offer further suggestions with this thread (now bumped up again) as you posted just before a major/scary holiday.
Higher gain (than standard 35dB) phono preamps are available in the the under $100/$$200 range (new), so if you don't wan't to put much money into it @ this point you still have options for getting the vinyl rig up and going.
You might be OK with a standard gain phono stage, but if you have to max out the volume dial, with such, the sound will be compromised as mating/matching is where it's at with all gear.
You need a "phono" preamplifier for EQ mainly and "gain" is only a a part of the equation.
Other (curently popular) higher gain phono preamps, off the top of my head, are the Jolida JD9a (WAY HIGH), Slee 2se, and perhaps the Cambridge 640p (not certain).