Age doesn't matter. Connections don't matter. All that matters is finding locations and settings that allow the subs to reinforce and extend bass response smoothly.
The more subs you have the easier this becomes, which is why the best method is a Swarm or distributed bass array approach with 4 subs. But if you are happy with what you have then great. That's all that matters.
Btw one reason you may be happy is that you're running your mains full range. Running them full range is in effect giving you three bass locations. Three is a lot better than one, which is what you will have if you follow the traditional and misleading old school advice and put a crossover and/or equalizer on your mains.
To answer your final question the main thing that will improve it a lot more from here is the addition of a few more subs. These can be more of what you have, or bigger/better, or smaller/cheaper. Which subs you use or even their quality to a certain extent or surprisingly even their location is much less a factor than the number of subs you use.
This runs counter to the majority of the conventional wisdom you will hear. So if you seriously want to improve your system sound in a way that will not in the least affect the midrange and up but will stupendously improve low bass while creating a feeling of immersion you never dreamed possible then you might want to do a search and read up on the Swarm, distributed bass array, and look for posts by me and Tim aka noble100 and especially Duke aka audiokinesis.
The more subs you have the easier this becomes, which is why the best method is a Swarm or distributed bass array approach with 4 subs. But if you are happy with what you have then great. That's all that matters.
Btw one reason you may be happy is that you're running your mains full range. Running them full range is in effect giving you three bass locations. Three is a lot better than one, which is what you will have if you follow the traditional and misleading old school advice and put a crossover and/or equalizer on your mains.
To answer your final question the main thing that will improve it a lot more from here is the addition of a few more subs. These can be more of what you have, or bigger/better, or smaller/cheaper. Which subs you use or even their quality to a certain extent or surprisingly even their location is much less a factor than the number of subs you use.
This runs counter to the majority of the conventional wisdom you will hear. So if you seriously want to improve your system sound in a way that will not in the least affect the midrange and up but will stupendously improve low bass while creating a feeling of immersion you never dreamed possible then you might want to do a search and read up on the Swarm, distributed bass array, and look for posts by me and Tim aka noble100 and especially Duke aka audiokinesis.