Need help on amp/wiring

So I currently have a box of 4 6x9 speakers on my tower. There are two pairs of speaker wire going into them and being fed off my five channel amp. The five channel amp powers the sub, in boat and tower speakers. I will be removing the 6x9's on the tower and putting up 4 Memphis HLCD speakers up. The Memphis speakers call for 100 watts RMS and are 2 Ohm. I don't really want to run new speaker wire through my tower and considered running the two tower speakers in series which would make it a 4 Ohm load, correct? I was thinking about running a PPi P600.2 amplifier to run just the tower speakers. Would this be the best way to take advantage of already having two speaker cables in place? Running two 2 Ohm speakers in series (creating a 4 Ohm load), does the amp still need to be 2 Ohm stable? And does it matter that the PPi amp is a class D. I was once told you don't run class D amps for tower speakers but it seems that class D is the better way to go and my NVX 5 channel amp is doing just fine under the observer seat.

Yes, running them in series will create a 4 ohm load. And no, the amp does not need to be 2 ohm stable.

Go with a 4 chnl amp. if you want to stick in that price point go with the ppi 4chnl

Mike, what is the benefit of running a 4 channel amp if I run 2 speakers in series to create a 4 Ohm? would you bridge the 4 channel so I can run the 2 speakers in series and use my pre-exhisting speaker wires running up the tower?

Unless you find a 1 ohm stable 2 chnl, you will only get its 4 ohm output which is then shared by 2 speakers. A 4 chnl amp is going to be an economical route as you will get its 2 ohm x 4 output. Yes, you can bridge that 4 ohm load and not have to run more wiring.