high pass filter options

Hi all, long time reader here- first time posting
I recently added a sub to my 2 channel system. I have been enjoying it for awhile but want to experiment a bit. Im working with Canton vento 9k bookshelves, my amp is Mcintosh ma5200 (various sources hooked up). the sub is a canton 12.3. room is treated as best as possible. I have always kept the sub crossover and volume low so it just be there to supplement the speakers. I want to instead run the speakers in high pass (100hz preferred) and keep the lows for the sub to deal with. I know its a debate to do this or not but figured to try it out. The speakers do not have a crossover on board as some canton's do, I just have them bi-wired straight to the amp. The amp itself is an integrated so im having trouble figuring out how to make it work without connecting an active external crossover. I have read Connecting an external crossover it may alter soundstage that im used to coming from the Mc. 
I don't want to run the speakers thru the sub, even if I could because the sub does not have a hpf output. It only has low pass input/out rca's and line level inputs. I currently have the sub tapped into the output posts of the Mc.
Options im considering is a couple rca line hpf crossovers from the preamp output of the amp to the pwramp input. Though with this option I don't know how I would then connect the sub as the speaker outputs would lack the low end that the sub is connected to. 
Another is to use a y-splitter at the preampt output to run the sub then connect the hpf after, but I am concerned this would degrade the sound in the end.
Lastly is it possible room correction or something like it could work? a more pricey choice like a lyngdorf I could run the speakers and sub independently while using its crossover, but again I would be investing in something that could take away the natural sound of the Mc amp. I want to keep it all simple as possible but cant figure this one out.
Any input or suggestions are much appreciated. Matt