The 840C User Manual shows an output impedance of less than 50 ohms. This is quite low, and will provide an excellent impedance match even with passive preamps.
I'm doubtful that a Burson Buffer would have any audible effect.
However, if you access to one without obligation, it's worth the experiment.
I'm doubtful that a Burson Buffer would have any audible effect.
However, if you access to one without obligation, it's worth the experiment.