Amp for tweeter in bi-amping
Well the tweeter is good for 105dB/W @1m according to the web site, but I don't think that woofer will keep up with that (But it very much depends on your box design)! 

Lets say you box is good for say 100dB/W @ 1m (Probably a bit optimistic), then you will need 5dB less power in the tweeter then the woofer, so somewhere around 20W or so. 

Now tear all that up, music contains transients and some of them are mostly high frequency, so I would just throw another 60W amp at the tweeter and scale the two with the output levels on your crossover to suit, that way you are less likely to clip the tweeter  which will likely damage it, (and the thing will likely sound somewhat better). 

Finally, if running off battery, you might find that lower impedance drivers work better for you, but that depends on your battery voltage and the output of any boost converter fitted.