The 33K resistors are part of the balance control, not "after" it. They make it act more like a pan-pot, maintaining total loudness while shifting the image from side to side.
That said, a shunt-mode control will have a variable input resistance - if the term is used in the usual way. (All these terms are used a little loosely!) In that case, the behavior of the balance control will change a little when the volume changes. Probably not enough to notice, just a technical detail.
p.s. What doess "amrg amtrans" mean?