Schiit SYS-49 and phono preamp with or without attenuator?

A simpler and shorter path, the signal goes through, is always superior in sq, such as cleanliness and detail of the signal, but the bigger question, ime, would be the output voltage and impedance of the phone stage, to adequately drive the power amplifier. Cd players produce an average of 2 Volts, and have lower impedances, which is enough for almost every amplifier. Many, or even most, phono stages, require an additional line stage ( more amplification ) for the proper operation of driving a power amp.

I have a choice to purchase a phono preamp - ss or tube - either with an attenuator or without it. What are your suggestions?

Get the phono stage without volume control, and with gain of >68db or higer, and an output impedance lower than 500ohms across the audio band into the 10k load of the Shiit Sys. Which the manufacturer of said phono stages should be able to tell you.
Then you will not need an preamp, with your amp into the 90db Tannoy Devons

Cheers George