OK so I have no choice but to use the CX100 in a vertical dispersion configuration. I will not turn them over onto their sides. As for my opinion of the sound quality of these speakers in an unmodified state; I mostly agree with your assesment over the telephone where you described the sonic signature as mostly Neutral, but with a slightly soft treble. However I do not agree that they are laid back. To my ears they are not Laidback and they are not Forward. I would class them as walking the fine tightrope between the two. You also critiqued them as lacking in Dynamics.
My apologies for my miscommunication. I was expressing that your speaker would lean towards the relaxed side ("laid back"), and be a bit wanting for dynamics when used for an HT. Of course, we are getting down to opinions and taste here. However, you seemed to agree with the rest of my assessment. Since you are willing to stand them upright, I'm willing to make a parts recommendation that will lean towards your desired result.
1, 2, 3, 5, and 6) Replace C1 with a http://www.soniccraft.com/product_info.php/gen-sonicap-68-uf-200vdc-p-443
, and confirm the small coil is an air core.
4) Increased output in the bottom two octaves will not be improved with a modified alignment. At least not for what you are after. Your 4" drivers are just not capable of moving the air at volume. This will require special attention to your sub selection.
Replace the Purple and White wire with http://www.soniccraft.com/product_info.php/neotech-solid-upocc-silver-in-teflon-23-awg-red-p-1879
. Replace the Yellow and Orange wire with http://www.soniccraft.com/product_info.php/neotech-solid-upocc-copper-in-teflon-18-awg-red-p-1580
. Replace the Black and Red with http://www.soniccraft.com/product_info.php/neotech-solid-upocc-copper-in-pvc-16-awg-yellow-p-1591
. Solder the terminal side of the cap directly to the input terminal "without" jumpering off the large coil. At the same time, solder the new 16ga wire that replaces the old Black wire to the same terminal. Leave enough lead on the terminal side of the cap to solder the new 18ga wire that replaces the old Yellow wire. You do not want to solder the wire right next to the cap. You want enough lead to place a heat sink between the joint and the cap if necessary. Solder the 18ga replacement for the Orange wire to the tinned part of the lead on the small coil just before it connects to the larger coil. Solder the 23ga White wire replacement directly to the appropriate side of the cap like you did with the 18ga on the other end of the cap.
Clean your solder joints well before and after. Make good mechanical connections before making good solder joints. Shorter lengths of wire is usually better, but leave enough slack for unstrained assembly. Further, I would leave/add the necessary 8-12% of length to make a twisted pair of the two leads that go to the tweeter, and the 18ga leads going to the mid. Lastly, be sure you have marked and followed proper polarity.