There's a difference in voltage between the Riva/eGo/Tornado and the KR8 batts. Scottbee discovered that the loaded voltage of a fully charged KR8 was an actual 3.7 volts while the eGo was only 3.1 volts.
This means a significant difference in heat (wattage) for the atty/carto.
I've been using LR 901 attys on my eGo to get good vapor and taste with most juices.
Throat hit seems to be a bit less than the LR 510 atty though.
I've found that fruit flavors taste best with a cooler running atty, while
tobacco and spice flavors are best with a hotter one.
Using a standard (3.0-3.5 ohm) 901 atty on your KR8 batt should give you good flavor.