Capacitor

Jantzen Standard Z-cap (it comes in 100mf 400v), otherwise most likely you should add up values to get the 100mf you are looking for. Depending on your space and budget, economic availiable alternatives would include Solen Fast, Audyn MKP Plus, Mundorf Mcap, Clarity cap SA. If budget is no issue then add whatever you fancy.

There's no easy answer. According to the laws of physics, the best cap is the one with a value closest to 100uF, (a twenty nine cent 101uF cap should in theory perform better than a one hundred dollar 110uF cap, both 100u nominal). However, considering the tolerances of capacitors, the designers had to settle on a nominal value of cap that sounds best to them, and reject values that fall out that tolerance. So if your expensive substitute falls out of that design tolerance, it may not improve things at all.

(I am assuming this is a commercial made speaker and not a DIY. If it's a DIY then the answer is: experiment with different makes)

What value  is important the uf or the vdc

No they are complete build units from Ascendo germany their flagship model the M5 SE with external crossover

Hi there,

This really depends.  With a value this high I have to assume it's a low pass filter.  If so it is likely to go to ground. If so these rarely matter as much as caps in series.  They DO matter, but it's hard to really judge their sonic worth as much.  To hear the difference here you might want to try a non-polarized electrolytic before you spend too much money.  Here's one that costs $2.

https://www.parts-express.com/100uF-100V-Non-Polarized-Capacitor-027-360

Try it and see if you feel it's an important capacitor in your circuit.

What value is important the uf or the vdc

The uF determines the frequency of the crossover filter (gross oversimplification) the VDC determines the maximum voltage.  If you apply too much it will short the capacitor and it will no longer work as expected.  That's a very high value for a speaker where I can't imagine ever needing more than 200 VDC rating in extreme high power speakers but with film caps it's hard to make a lower voltage cap sometimes, do don't go looking to optimize this. 

Best,

Erik