Gaby,
Didn't do the defretting myself, to be honest - but indeed like yours it's a koa Epic. I think Mica once mentioned that koa is a favourite at Alembic for fretless basses ...
To my ears, the bass still has the same tone of voice as before, just that the articulation has changed - a lot.
TI Jazz Flats are giving me a grand, blooming low end response on the E string, which in retrospect didn't exist when the frets were still on it. Pluck it the right way and it will give you a nice upright-like tone. As with all Alembics, the way you hit the strings can produce very different sounds - and it allows you to dig in deep. Especially playing over the top frets, you can really make it sing.
Obviously you lose some of the sustain, but that's a natural trade-off. You will need to make changes to the nut to make the strings sit lower - I still have to take a file to the underside, as the nut has been floating without the separate base plate underneath ........ uh, if you find this confusing then take a closer look at the nut, as it is one of those features unique to Alembic.
Fret not, enjoy!