i actually like kis, it is nice and fast comparing to version 6, i have it on one machine. everything but firewall is pretty much turned off most of the time tho
as for original question, there is a setting "maximum compatibility" in firewall settings that you might want to check if using p2p. besides that, based on how powerful your system is (or isn't), you might want to turn off live file scanning and scan files that you don't trust after they are downloaded.
as for firewall, nothing beats hardware router or separate internet box/router. running on debian of course
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