I have a 7100/80 with a NuBus ProTools setup, though dismantled currently. I was able to get it working with cracked software from here and the Garden. There are some effects, but you can only run two at a time on a basic two-card set since a lot of the DSP is used for mixing. At least, that's how it is for me - contemporary reviews make it sound like you can run more, but I haven' t been able to. At any rate, these are early-generation DSP effects, they're not very high quality and depending on your tastes might not be very interesting. The Nubus cards are also RAM starved, the longest delay is less than a second as far as I remember. I like my setup, though, it's cool to have this under System 7.
For Turbosynth, you don't need Protools, there's only one function that runs on the PT cards, if you don't have it it just gets disabled. It's not a very interesting effect.
For me, the jewel of this ecosystem is actually the SampleCell card, which is an 8-out sampler that integrates very well with Turbosynth (you can make it load sounds automatically as you edit them in TS), and with the TDM mixer. At least for me as more of a "build electronic music from scratch" than "record bands" type of person, that is a setup that has some interesting qualities as a whole. You can buss its sounds through the TDM effects before going out throw the ProTools audio interface, along with the audio from ProTools, and all in all it becomes a lot like a modern DAW setup, only rather primitive and with the black and white System 7 klunk, which I personally think is very cool. I'm currently using my G4 + RME-based system but I miss the Nubus setup at times.
NB: If you want to use the TDM audio capabilities, you need two drives: one to boot from, and one that's connected directly to the Protools core card. Also note that not all "black" audio interfaces are compatible with the old systems. You want the very early ones. I have an extra 882 I could part with for a very good price (I'm in Europe).