It is, I've tried it.
That into a Topping A50S would give you a good sound - for around £270-£290 total?
I own an A50S.
However, having tried Topping's A90D model, I can assure you that would really allow you to appreciate what your headphones can do. - with decent recordings (considerably more expensive, so maybe an eventual upgrade idea, since you're sticking with your headphones
).
Depending on the spec of the amp you decide on, the balanced option is worth considering. but I wouldn't pay too much for a balanced cable.
I believe Focal use just standard 3.5mm jack plugs (albeit with slimmer barrels maybe) at the earcup ends of the cable.
That makes DIY construction of a high quality balanced cable cheap and relatively easy if you've got a soldering iron - especially if you fit an XLR, rather than Pentacon connector at the amp end of the cable.