There are definitely some through hole components on the 300 series, based on the internal shots here:
And I think much of my XS3, old classic, used surface mount. In fact I think the main difference between the MM stage in the XS3, and the same stage in the SN3, is that the latter used through hole and the former mostly SM.
I think Naim have been moving to SM for a while, and used through hole for key components in higher end boxes.
