Krell KAV 250 A

Going from a 300i to a 250a driven by the 300i's preamp will certainly add some slam factor & dynamics to your rig. The 250a that I had seemed to never run out of steam; it has considerable headroom & sounded quite detailed esp. for an av class product. The disadvantage is that you'll then need a pair of quality interconnects & another good AC cord for the amp, in addition to the one that you're hopefully already using for your integrated. Of course you'll need to disconnect the signal links so that you're not driving the 300i's amplifier stages into an open load condition, & bear in mind that any idle current consumed by the amp stages will be wasted energy unless you can locate some internal rail fuses & remove them. No you cannot combine the output power from the integrated along with the 250a or any other amp. You could use the 300i's outputs for driving a separate pair of speakers though.

Bryan certainly makes a good point. Not being familiar with this 300i piece myself I don't know if in fact there are outboard connectors that allow separating the preamp stage from the poweramp section; in fact these connections may not even be available at the rear panel, but only inside. I had previously checked on Krell's website, but I don't see it shown there.
Certainly any stock power cord will allow a component to play music, but not at its' optimum by any means. Just stick with whatever you're comfortable with for the time being; I only mentioned this because if I had kept my 250a & tried to tweak it with better cabling, then I might not have ever sold it. But I didn't believe in any of that "nonsense" either at the time, & probably made a mistake due to my ignorance.

here's another issue: was thinking that if the 300i does not externally link its preamp output section to its power amp input section, then you have no external access to variable-level preamp output to drive an external power amp anyway. You cannot use the tape monitor output (even if available) because it runs at a fixed level, but you need variable of course.