Ok, I have the little Radio Shack SA155 amp out on the
bench doing nothing. The SA155 uses RCA jacks for speakers
as well, plus it has a 3 way switch for input selection
including phono preamp.

Are we saying that a small plate amp should be a part of the
project? PE has those for $30 as does MCM.

If I had a tuba 18 would these same issues apply? From the
audioXpress writeup Fitz did on the build, there's not much mentioned
about hookup that I recall-- and no plate amp showing anywhere.