To get louder, you would have to spend money, no free lunch.
The easiest route, add another amp, either a 4 channel that can be bridged to get about 150X2 or a two channel that does about 150X2. Then bridge your alpine so that it is wired to produce 150x2 (see manual or markings on the amp for speaker connection). Then you should be near equivalent to your friends setup in terms of overall loudness. The amps might run cooler too because you might not be straining them as much now that you have increased the potential power capability.
You might have to make sure your power wiring can support the extra current needed to power multiple amplifiers. There are charts around the web that can tell you recommended wiring/length for a given amount of power.
But now you know and hopefully can use this knowledge in the future if it's not something you will change now.