See if you can at least rent or try the RBI, it is better than any other DI listed here with the exception of one that hasn't been listed yet all hail the almighty Avalon U5 Class A DI Preamp/EQ. easily the best freq response :
Frequency Response, -/+0.5dB: 5Hz to 100kHz
Frequency Response, -3dB: 1Hz to 500kHz (input band limited)
