If you have two speakers paralleled \per side, you are at 2-ohms per side, usually less. When use an amp in bridge mode with that parallel load, you show each amp channel 1-ohm, usually less. That is quite close to a dead short...
If you intend to keep that amp on the tower speakers, you can do two things:
1. Wire the speakers in series to an 8-ohm load and put that load on half of the amp in bridge mode. Same thing for the other side.
2. Run an extra set of wires up to the tower so each speaker has its own amp channel.
Both options will "show" each amp channnel 4-ohms, and both will get roughly 75 watts to each speaker. The second option is better, as you get more copper in the system with an extra run of speaker wire.