active X-over

I think the only way to tell would be to take some measurements. I don't think I tell purely by ear.

Typically the biggest problem in full range free standing speakers is the broad suckout somewhere between 100 and 300 HZ - it can be a real devil of a problem and it is near universal too. In some cases a 12 db crossover on the sub may work better than a 24 db filter typically from a pre. You need to try it and see...but I'd recommend measurements and trying all kinds of positions for your sub too - ultimately positioning may be the most important factor overall...

At least if your test provides a null result it will have been worth it - just the peace of mind knowing you are not short changing yourself with pre. I have done tons of of A/B testing and it helps to use the remote and to try and do things blind if you can...often sighted tests result in a preference whereas blind tests result in a shrug of the shoulders...