Best Speaker with Krell KAV300i

Try getting a speaker that has a slightly darker presentation. Bright sounding speakers would not be a good match.
Also stay away from tube friendly speakers like Proac. The Krell will work well with Planar/Ribbon type speakers.

The Martin Logan SL3 mates well with the Krell300i and sells used in this range.

I have used ML Aerius, B&W Matrix 805 and Dynaudio 1.3mkII in the past with this amp. I liked the B&W best.

Martin Logan and B&Ws are the best combos with krell gear. I was just in the factory last week and they had a pair of martin logans in there and they will also tell you B&WS