While you say that you are not worried about your liver please remember that it isn't safe to take that much APAP in a day. APAP is horrendous on your body in doses such as that and can cause many health risks. An APAP OD is a slow painful way to die, with your organs slowly atrophying from within.
Please think carefully before doing anything like this.
As to the DXM, redosing can have a plethora of different effects, some people reporting a stronger, longer duration trip, while others have reported no effects at all.
I'm not the best authority on DXM so I'll leave this one open to allow someone to better answer this for you.