Easy enough. It works the same way as with any 3rd party SSD, fusioned or not. Trim Enabler.
i have a Sandisk SSD 256Gb along with the 1Tb stock spinner, fusioned to 1.25tb Fusion drive. Trim is enabled and everything is fast and awesome.
I too am an audio guy btw, and while i'd LOVE a mac pro, it cost too much. And you don't need GPUs for audio work. If apple made a MacPro with just one GPU (or even iGPU only) for Audio pros and trimmed $500 off the price... ...it'd still be way too expensive
Bare in mind that not everyone lives in the US. Where I'm from a base Mac Pro is roughly 6 avarage 'decent' salaries, 1) because median salaries are lower than in the US and ironically 2) because Macs here cost an avarage of 50% MORE than in the US. base nMP is around $3950 ina an authorised reseller here. MacMini is really the only viable Mac us and we can defo use that quad core chip.
I am also confident however this is due to intel and that it will be back (unless intel decides do **** us over) with either broadwell or skylake...
I also work for a software developer btw, and we have about 5-6mac minis as the go-to development machines for xcode. I think saying that the mac mini is a consumer only low-end mac is a bit myopic. It dfinitely has a lot of value to many buisness users and in large volumes, and I'm sure apple knows this.
sorry for the epic long post...