The TX81Z is a good all around module for FM synthesis. The voice programmability is more limited than it is for the DX7, but this also makes it easier. It uses the 4 operator/8 algorithm FM engine that you see on the lower end models, but the ability to select from 8 different waveforms for each operator makes it easy to change the character of the sound without having to balance out a bunch of parameters to keep it in tune. This is what makes it so easy to make tons of different bass sounds on it. Most of the parameters are simpler than they are for the DX7.

There aren't quite as many operator frequency ratios available as there are for the DX7, but it's not really something you would miss, except for maybe the maximum ratio of 25.95, whereas the DX7's ratios go up to 64.00, which is high enough to bring all the dogs in the neighborhood running.

The EG's are ADSDR envelopes with ranges of 31-31-15-31-15, which isn't as complex as the 4 stage envelopes of the DX7, but most sounds don't go beyond this type of scheme anyway.

You can't set the scaling breakpoint or curve, so it acts like a negative linear curve with the breakpoint set at the very lowest note. In other words, you can only set how quickly the operator level tapers off as you go up the keyboard.

There aren't as many waveforms for the LFO, there is only triangle, square, saw up and S/H.

The edge that the TX81Z has over the DX7 is the 8 part performance mode, which can use 8 different sounds in layered, split, or alternating configurations. The unit has only 8 note polyphony, but an 8 layered bass sound can be a pretty intense sound. Take your favorite bass sound, make 7 small variations of it and stick them all in a performance. You'll get a sound your mother wouldn't even want you listening to.

It also has a MIDI delay, panning and single note chord effects, and microtuning capability. It's actually a very well designed unit.