Using on-board amplifiers instead of external amplifiers
The reasons that external amplifiers were used are:

1) Simplicity/cost of the Eval board

2) Wide range of possible SiPm signals - under high pulse illumination SiPm signal, even the 'fast' one might be very large (talking ~1V) 

To preserve the bandwidth = pulse shape  of the 'fast' SiPm of 6mm size, you   need roughly around 300 MHz or so. It is a bit on the limit for the opamps, it is easier to use RF-amplifiers ( the 'fast' is anyway AC coupled by nature with few MHz low freq cutoff ).

You can use e.g. BGA2818 or similar, however one has to be RF aware when routing the board (which is not that difficult). You can perhaps acquire some Eval boards  for them first and solder bigger coupling caps there to improve low freq cutoff.

Also, you should have a look at boards like this.