First off the VR-4s reach down to 20hz. So a sunfire junior will not really help you as it will only reach down to about 28hz. You will have to go to a larger driver 12 inch Sunfire Signature series or a 15 inch or larger driver like bagends.
If you use the same terminals on your amp out to the high in of most powered subwoofers this will work for variable volume. Or use the tape out (non variable volume) if you listen to your music at about the same level every time. Both will work.
The "high in" is a passthrough design in most quality subs. So it really will not draw any significant current from your amp. It just means however that you have to double your speaker cables which might in some cases mean more money than its worth.
You also do not mention the room size, but I would guess large. This will affect how much air you want to displace.
Try looking at a MKV-12 earthquake, they are usually discounted on audiogon and will go down to about 18hz or the MKV-15 (much harder to get) it will go down to about 14hz flat.
If you use the same terminals on your amp out to the high in of most powered subwoofers this will work for variable volume. Or use the tape out (non variable volume) if you listen to your music at about the same level every time. Both will work.
The "high in" is a passthrough design in most quality subs. So it really will not draw any significant current from your amp. It just means however that you have to double your speaker cables which might in some cases mean more money than its worth.
You also do not mention the room size, but I would guess large. This will affect how much air you want to displace.
Try looking at a MKV-12 earthquake, they are usually discounted on audiogon and will go down to about 18hz or the MKV-15 (much harder to get) it will go down to about 14hz flat.