As Mofi indicated, you won't hurt anything by using a y-adapter. Here
is one such adapter. There are others that are available in the form of short lengths of flexible cable.
The impedance considerations George referred to can affect tonal balance under some circumstances, at least slightly. I couldn't find specs or measurements on the output impedance of the PV10B, or on how that impedance varies as a function of frequency (which is important, but is usually unspecified). And the input impedance of whatever power amp you are using is also a factor. As are the lengths of the cables from the preamp to both the power amp and the subwoofer, and the capacitance per unit length of those cables. I did, however, find the following statement about the PV10B, which provides some degree of confidence:
Cathode follower outputs in both stages provide low output impedance, making the PV10B compatible with nearly all installations, including those requiring long lengths of interconnect cable.
So my guess is that if the input impedance of your power amp is not particularly low (e.g., as long as it is not much less than say 25K), and if the lengths of either of the cables from the preamp would not be unusually long, you'll probably get good results. If any adverse sonic effects occur, the most likely symptoms would be rolloff (weakness) of the deepest bass (due to the impedance issue) or of the extreme upper treble (due to the cable capacitance issue; the signals received by the main power amp may be affected at high frequencies by the capacitance of the interconnect cables to the sub as well as the capacitance of its own interconnects).
In any event, you won't hurt anything.