E-Stat: Actively buffered tape outputs are pretty rare on regular stereo pre-amps, integrated amps and receivers, even more so on the more classic designs - in fact most tape-outs just sport a little decopuling via a resistor in series per channel. And the hk725 belongs to that majority that doesn't sport actively buffered tape-outs.
So other than the extra 1k resistors (in this case) in the path to the tape outs, there's little technical difference between a parallel y-connection from the line-outs of the CD player and a connection through one hk725 via tape-outs to the other. However, there's a big difference in functionality, 'cause in the latter case the second(ary) hk725 couldn't be fed by the CD player independently of which source is selected on the first hk725 anymore.
And for the record, Wayner's claim above, that "almost all preamps will short out other unused inputs", to my experience also is anything but realistic.
z-a: Spec says 23 kOhm input impedance for the line inputs - so even driving two hk725s in parallel should be aboslutely no problem for a typical CD player. Especially in case the distances from the CD player to the two hk725s wouldn't be all that short (read: more than some 3 metres max. to each side), you should make sure that the y-cable-solution is made of a reasonably low capacity cable type, though.
Greetings from Munich!
Manfred / lini