You want to leave your receiver on 8ohm, even if you have a mixture of 4, 6, or 8ohm speakers.
My Denon also puts my 80's and vp150 on large, but I change this to small for all speakers and 80hz crossover on the receiver to manage, sub crossover on bypass.
Keep in mind that with your 60's set to large, they will be receiving the signal from your other speakers below the crossover, unless your using LFE+Main mode, then your sub and mains will receive this.
Generally, it is better to let your sub do the job it was intended as it can move more air easily and efficiently. With a setting of small and a crossover of 80hz, your 60's are still receiving signals below 80hz as there is a slope/blend (handoff) to the sub, it does not just cut off.
