I like to set things at the middle and adjust things as needed. It's definitely a balancing act. You have posted here before but it helps if post all the equipment you're using to make it easier to recommend.
my windows volume is always set to 100% and i adjust the ambient volume with the knob on my receiver. if i want certain applications to be lower or higher volume than others then i adjust that volume setting in those applications.
i generally find that most convenient for me.
however, if you do not have a volume knob close by or if it does not have a remote if you are farther away then perhaps adjusting the windows volume may prove a bit easier for you.
what works best depends on your particular setup and personal preferences.
Yeah, I usually have my windows volume at or near 100% because it doesn't effect sound quality. I don't remember what his setup is from previous post but I was thinking he was referring to various audio products connected to a source like a receiver/pre amp. For example don't wan't to turn up gain to high due to distortion.
What cassette decks are you using? I have some old Nakamichi decks but what I'm guessing is that you're referring to the the output slider on the deck?
Here is a pic of this model that I own. Notice the output slider. You can pretty much crank it up or down depending on how much gain you want. It just takes some experimentation to find the best sound. It isn't really a volume control but more of a signal strength control.