Y connector from pre-out to powered sub and...

This will not present a hazard, but it will be very slightly less than ideal sonically - just a very slight (and I believe quite tolerable) whitening up of the highs in the CJ. The determining factor will likely be whether or not the CJ actually has enough juice to to drive both devices from the same output. Very often consumer gear ends up lacking enough drive to make this sort of thing work, pro gear often has less trouble, but sometimes you run across HiFi gear with enough voltage. You'll very likely simply have to try it and see. The two loads will not really see each other, rather the CJ will be seeing both loads at the same time. If it all sounds perfectly acceptable, except for the minor quibble with the highs as noted above, then you should be good to go. If the CJ isn't up to the task, then it would only likely be a matter of the sound quality of either, or both, of the add-on equipment temporarily not being up to their usual standards for you...there should be no harm to anything being done at this point, but it will be telling you that the CJ is being asked to do more than it can do and that this idea, at least for these two particular add ons, won't work. Just remember that the reverse application of trying to feed two outputs into one input is not a workable idea...this can double the load going in and can create an overload condition that can sometimes cause things to fail (whether outright or over time) but splitting is not considered hazardous, it's just that it's sometimes just not feasible.

You will need to find out the input impedances of all the equipment to ensure you don't drop below the minimum cumulative output requirement from the CJ. Tube pres are usually not very flexible or forgiving in this regard.

Agree with Spinaker. Had similar issue with my ARC Ref 3 and 5 linestages. Pull my threads for more complete explanation and fix. I suggest, as did I, that you call the factory and ask for their advice. The issue is whether you may be overloading the pre's outputs. Btw, in my case, I would have shorted the outputs, so I needed a buffer.

More often than not, when a preamp provides two sets of RCA output jacks they are simply wired together just inside the rear panel, as opposed to being driven from separate output circuits. So chances are you would be driving all three destination components with the same driver circuit in the preamp.

Along the lines of the earlier comments, how well that would work depends on the output impedance of the preamp (the lower the better), on how that output impedance varies with frequency (the lower it is at all frequencies, and the less variation there is, the better), on the sum total of the capacitances of all three sets of interconnect cables (the lower the better), and on the input impedances of the three destination components (the higher the better).

I couldn't find specs or measurements on the output impedance of the preamp, but I did find on this page the following statement:

... the audio circuit of the Premier Ten consists of a single triode amplifier direct coupled to a triode cathode follower. The low output impedance of the cathode follower permits the use of the Premier Ten with highly capacitive amplifier interconnect cables without attenuation of the high frequency information.

That is encouraging, and suggests that there will be no problem in the highs as a result of the interaction of preamp output impedance and the total of the three cable capacitances.

The other usual concern is that if the preamp's output impedance rises significantly at low frequencies, to levels that are too high in relation to the combined (paralleled) input impedance of the three destination components, the deep bass could be rolled off. Based on the quoted statement, I would guess that you'll be ok in that respect, but the only way to be sure is to get specific guidance from CJ, or to somehow ascertain what the output impedance of the preamp is at the frequency for which it is highest (which is often 20 Hz).

The overall input impedance of the three combined loads is equal to the reciprocal of the sum of the reciprocals of their individual impedances. In other words, if the input impedances of the three loads are represented as Z1, Z2, and Z3, their combined impedance as seen by the preamp is:

Ztotal = 1/((1/Z1) + (1/Z2) + (1/Z3))

Ztotal should ideally be ten or more times higher than the output impedance of the preamp, at the frequency for which the output impedance of the preamp is highest.

The suggestion by Bruce (Bifwynne) of a buffer, such as the one that was made for him as described in some of his other threads, would be a good solution if that impedance matching criterion is not met without one.

Regards,
-- Al