Let's say you start with a pair of stereo speakers. Then add a woofer. Then add exciters.
Should the woofer be powered by the 2.1 amp that drives the stereo speakers? Or a 2.1 amp that drives the exciters?
If the woofer is added at the same time as the stereo speakers it's probably already powered by the same 2.1 amp. But should it be changed over to the 2.1 amp powering the exciters when they are added?
Would it depend on the signal driving things? IIRC you can split the sound & send the mechanicals to secondary audio device.
IOW do you want the woofer enhancing the audio sounds from the backbox or adding haptic feedback along with the exciters?
If not using 7.1, leave the woofer on the existing backglass sound amp and add a second 2.1 amp for the front exciters positioned near the flippers. Split the mechanical sound to the second amp in VP audio prefs.
This will give you the basic starting point for you to "dip your toes" in.
If you like what you hear and feel, then you can add a rear position "audio" sub to that amp, or add yet another amp for rear exciters and rear audio sub (see my diagram above, or in the thread that I linked if the diagram does not display here). These will all work off the second sound device output from your computer, provided that you split the output to feed the two amps. Once you balance all the amp volume levels, the effect is quite amazing..... This is how I played for over a year and it was absolutely fantastic, but it was only Left/Right positional and not true "surround" sound. Any surround effect front / back was just as illusion of balance between amps and visual input of the ball.
If using 7.1 in VPX Beta, then you can use the same setup as above and each of your your three amps plugs into a different channel output from the 7.1 card. In this case, your subs are all working independently.
as Rob has done, use the Bass routing feature of your system and the surround will feed ALL bass via just the one main sub. This negates the need for the purchase and install of the additional sub(s) as seen in my diagram.
It's a very configurable system and it's a system that you can start small and build on. That said, it's my recommendation that you jump right into 10.4 beta and 7.1, as directional sound & feedback is a game changer and can be used in place of DOF, or to at least minimise DOF installs to just blowers & LEDs. (although I have my LEDs sound driven too, but that's another thread on its own)
Based on a stereo output and not 5.1 Dolby surround :
The exciters do not have the volume of the regular speakers, so I would place them on their own separate amplifier (same audio source), provided that it has a volume control. try a Pam8610 Audio Stereo amplifier. They are ~$5 USD and provide >10 watts at <1%THD @12V (4 ohms) and a volume pot. I would like to know what Rusty's recommendation is on this too, as I know that he has done lots of experimentation on this also.
Re volume... the exciters that I am using are loud! I live on acreage with my closest neighbour is about 150m away.... but if I lived in the suburbs, I'm pretty sure that I would get complaints from the neighbours lol