It should be OK. Check to verify the Prima Luna's input impedance is much higher than the output impedance of the CL-15. It should be so much greater that cutting it in half this way would still result in a big difference. This prevents the double connection you propose from demanding too much current from the CL-15, which would otherwise affect the sound and maybe the circuitry. (--Just like a speaker with too low an impedance starts to look like a short circuit to the amp.)
I would recommend avoiding the retermination of the APCs, because this may change the electrical characteristics and hence the sound, which you like as-is. Instead, consider a Y-splitter at the CL-15. You can buy cheap ones from Audio Advisor or Radio Shack; or, I have bought custom Y-splitters from Cardas on special order. (These are not cheap.)
I have employed both approaches with good results. In one system, I have a Mark Levinson 390s driving a Pass Aleph 3 and a powered subwoofer (Sunfire), using a Y-splitter. In another system, I have the XLR outputs of a Sony SCD-1 going directly to a line level preamp and the RCA outputs of the SCD-1 going to a Manley Steelhead's line level input (so I can enjoy the sound of the SCD-1 through the Manley's line stage). Both work fine.