so, just a disclaimer, ive never done this to this chassis before, but it looks to me like these changes would help:
C80- .001uF (TX)
C81- 1uF (TX)
C83- 1uF (RX and TX)
C82- 100pF (RX and TX)
C75- .47uF (RX)
C94- 470uF (RX and TX)
joedirt is right about the audio transformer choking the bandwidth, but you should still notice some improvement.
the parts values i chose for the changes are just guesses.
the changes should be done one at a time, and the effects noted.
the general rule is to increase the series capacitance and decrease the parallel capacitance, which is what ive done in the changes i suggested.
for example, i chose 1uF for C83. you may find that this is way too bassy, and you might want to try a .47uF, or maybe even a .22uF capacitor.
one thing to note here is that electrolytics should not be your first choice.
ceramic and mylar caps are better for audio tailoring.
good luck, and please do post your results for the benefit of others who my run across this thread in the future.
LC