The real interesting stuff behind the 1.79MHz filter is that it builds an "interference" at the (starting)3.58MHz resulting waves.
Thus you don't hear the absolutely high frequencies, just the "interferencing" sound. which results in a sawtooth wave by standard.
Could be interesting to have the tool changing the channel pitch fast enough, to get any other resulting wave coming through.
You know: An ascending sawtooth followed by a descending sawtooth is a triangle
As you might get from my POKEY edits, waveforms can be build all over the "musical range" .
What is really missing, is the controlled replay of "channel addition" sounds. This is the only way to put more power to the created wave and to cut the high frequencies.
Listen to the start of this tune...
(it starts very "volumetric" ) .
This type of channel wave addition is only to control fully, if a "pokey reset" can be placed on specific points.