Are any other methods of mult-wave sampling? For example if I wanted to replicate an snes trumpet sample on the n163 I would use audacity and copy 1/60 of a second and the results would be ok ish. Getting it to loop is a whole other pain in the neck. Thanks

HertzDevil has some utilities for FamiTracker in this repository. https://github.com/HertzDevil/ft-misc-utils/tree/master

WaveGen is what you want to look for, although I have not personally had used it in a long time, so you might need some trial and error with the parameters it needs.

Of course being a FamiTracker utility, it will only produce a .FTI, so if you need to use it with Furnace instead you'll need to do some manual conversion work, but that shouldn't be too difficult I think.

FamiStudio has a fairly capable .wav to wavetable conversion function, so you could make your instruments on there and export them to a famitracker text file, though i do not know how or if you can convert a .ftm into a furnace-compatible file format
even if it's possible, beware that FS imposes a limit on the wave count based on how many points per waveform are used for homebrew reasons, so you can't have many large waves in a single instrument

there are some tools listed on the nsfplus format and the dedicated N163 tools lyceum pages. be warned that none of the options for resampling/sample-conversion are great. (the synths are really cool tho!)

the one I personally used a few years ago was just called "wavetable" - doctorn0gloff was kind enough to set me up a google colab workspace for it, also linked in the lyceum, so you could give it a try relatively easily. I killed like two days of my life just trying to get a bunch of SNES samples sounding clean and functional as N163 multi-waves. I was only moderately successful, especially since I have to transpose a lot of my instruments (I had trouble with the tool's root pitch function), but I effectively made it so that I never have to do this hell process ever again, so it kinda sorta worked.

the other really important thing to keep in mind is that you will be severely limited on instrument space if you need to export to .nsf - even moreso in Dn-Fami ver 0.5+! even if you keep wave size/count fairly modest, you can rack up storage space and get an "instrument overflow error" very easily. on botb specifically this means they're better suited for the famiplus format. not totally unusable, but in the nsfplus tracks where I've used N163 it's basically been like 3-4 N163 instruments, DPCM and virtually nothing else instrument-wise, necessitating tracking all your effects and volumes in-line.