OK for speaker cables you have several options. You can play the system continuously at rather high levels when no one is home; allow for some consideration if you have pets though. You can use a break-in box, but the caveat here is to use caution if you have MIT or similarly terminated cables, because (some) breakin boxes apply DC, which will blow up the terminations, per MIT. You can setup a cheap garage or basement system & play the radio; face the speakers together & wire them out of phase to cancel some of the racket. You can make yourself a 4-ohm or 8-ohm dummy load out of some power resistors (must know ohm's law of series-parallel resistances to do this) or maybe just get 2ea. (1 per channel) 5 ohm or 10 ohm 20 watt power resistors, whatever is readily available, and some healthy-gauge clip leads. Cliplead the dummy loads to the ends of your speaker cables that you are breaking in, & absolutely use some electrical tape to ensure against short circuits! Death to your PA if you're not careful... Crank up the power partway & check the loads at intervals to ensure against overheating the resistors. They can be allowed to get nice & warm, but not blistering hot. Don't burn yourself, & don't look here for liability if you mess up (this is only my disclaimer for self-protection, even though it's free advice). The question regarding digital interconnects is a bit different. You must repeat-play the CD player, but it's not necessary to listen, or have anything other then your outboard DAC connected as a load termination. DAC power may be on or off - matters not.
