I've run RCAs and digital coax simultaneously out of several CDPs and DVD players over the years (including a CAL CL-10 and CAL Icon II) with no ill effects to the players. I don't think I've been compromising the sound either, not noticably anyway.
The RCAs have gone into my integrated and the coax into an outboard DAC, allowing me a choice of listening to the players' internal DAC or the outboard DAC.
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.
The CAL Delta transport has 3 outputs, and the manaul specifically says all three are isolated and may be used simultaneously. I don't know if CAL extended this thinkng to other products or not. My guess is you are good to go with the caveat of cable retermination as James mentions.
I tried hooking up a pair of XLR ICs and a pair of RCAs out of both sets of outputs from the CL-15, but the preamp of my integrated amp, an Electrocompaniet ECI 3, may be shutting down the RCA input circuits. I'll try it on the PrimaLuna Prologue One amp next. That's the primary focus anyway, but the Cal player has been in the other system and it was convenient to start there.
The PrimaLuna One's input impedance is 100k ohms, Input sensitivity 300mV. Viz.
Description: Single-box line-level tube preamplifier and push-pull tube power amplifier. Tube complement: two each 12AX7A, 12AU7, EL34. Inputs: 4 single-ended. Output power: 35Wpc into 8 ohms (15.4dBW). Voltage gain: 20dB. Output impedance: 4 or 8 ohms. Frequency response: 20Hz30kHz, ±0.5dB. Input impedance: 100k ohms. Input sensitivity: 300mV.
The CL-15's output impedance is 50 ohms (usable into passive controller).
Does this seem doable? The P'Luna's impedance is listed in kilo-ohms, while the CL-15's impedance is given in ohms. My newbie's provisional conclusion, then, is that there should be plenty enough of difference still.
However, one logical question--which component's impedance will be cut by half? Your language suggests it will be the P'Luna's, but my beginner's mind says it will be the CL-15's. If this is the case, then there may be too huge a difference created by the double hook-up, dropping the CL-15's output impedance by so much that the signal coming in from at least one of the outputs of the CL-15 will look to the P'Luna like a short. This happened with the ECI 3 amp already, although I realize I'm speaking hypothetically with regard to the P'Luna. I still haven't tried it.
Bblilikoi -- Based on your numbers, I think either of the contemplated hookups should be OK. The CL-15's 50 ohm output would normally be looking at a single 100,000 input on the PrimaLuna. This is a high ratio of 2000-to-1, quite satisfactory. If you double the number of inputs used on the PrimaLuna, you are doubling the current required from the CL-15, or cutting in half the impedance presented to the CL-15 by the PrimaLuna. The result would be equivalent to a still-quite-high 1000-to-1 ratio. Should be fine.
The Electrocompaniet may have had a sensor relay that chose the XLR input, shutting down the RCA. It sounds like both the XLR and RCA were plugged in to the same input source selection (e.g., "Source #3," which would have both XLR and RCA sockets), in which case the preamp would be forced to choose one and mute the other. To avoid this in the future, try using different input source selections if possible (e.g., "Source #3" for XLR and "Source #4" for RCA). Good luck.
Thanks. Actually, the EC amp has different source selections for each type of paired sockets. I think, then, that the XLR and RCA ICs were inputting via different source selections as well as sockets, but the EC amp still shut down the RCA input signals from the CL-15 in favor of the XLR.
I'll try the "double-trouble" ICs experiment with the CL-15 and PrimaLuna this weekend.
Going back over this problem, I've made many changes. ICs which may have sounded great in combination with the system I started with, don't perform the same as the system has evolved--a familiar process not news to anyone, I'm sure. But the radiance of the Analysis Plus ICs diminishes somewhat with the new system:
Cary SLI-80 integrated amp;
Audio Refinement Complete CDP;
Sonus Faber Grand Piano speakers;
Audience Au24 speaker cables;
Audience Au24 ICs;
PS Audio Plus PC (amp);
Shunyata Diamondback PC (CDP).
I found switching to Audience cables created more openness with this system and the radiance I'd formerly heard with the AP cabling diminished with the different equipment. Finally, my instinct is the Atlas Titan RCAs, certainly a premium interconnect, are worthy of re-auditioning, as they scored very high in dynamics, detail, and speed in the prior system, creating a very bold sound with the complex and rich textures of orchestral symphonic music, Ellington's lush harmonies, and the swaggering saxophones of 60s jazz. I'm excited to try them again as the system has evolved.
Did you get a chance to re-audition the Atlas Titans? How do they compare to the Audience Au24's? I'm currently using Audience Au24 IC's and speaker cables (single run with Audience Au24 jumpers) and like them very much. I was just curious how they compared to the Atlas IC's.
I haven't had a chance to re-audition the Titans as I've completely changed the system(s):
Cary SLI-80 integrated amp;
Cary 303/300 CDP;
Audience Maestro ICs;
Audience Maestro speaker cables;
Sonus Faber Concertino speakers with stands.
I'm at present working on settling in a new reference system with all tubed equipment. I plan to buy Audioquest Cheetah ICs for this system and stay with Audience Au24 speaker cables for the time being.