Interchangeability of amps is generally not desirable for a subwoofer.
All of the major subwoofer companies select the amplifier to ensure reliability of their subs. By that, I mean the amp is designed/selected to match the parameters of the driver and usually has some type of limiter to ensure that neither the sub nor the driver is overloaded.
Also some form of EQ is often applied (part of the plate amp unit) to improve performance.
Most of the major subwoofers are damn near bullet-proof. Tom V. of PSA said (not an exact quote) "Don't take it as a personal challenge, but it would be hard to blow one of our subs". I think SVS, Hsu, Rythmik would probably tell you the same.
When Jman reviewed the lowly ~$130 Dayton Audio SUB 1200, he was impressed at how, when pushed to its limits, it did not make any nasty sounds or lose composure:
Since the SUB-1200 seemed virtually impervious to deleterious behavior I decided to push it with some of the most demanding blu-rays in my collection. To my utter surprise it held its head high and said "no, I will not falter". Most of the really torturous movies I watched weren't quite as fulfilling as they've been with some other
subwoofers in the past, but this 'cheapie' never put a foot wrong. In retrospect I probably should have chosen different test material; gut-wrenching bass is not this subwoofers forte, yet I treated it as though it was. To a certain extent it almost became a quest to see if I could make the SUB-1200 lose composure, but I was ultimately never able to do that. It's almost bullet proof in that regard, and I tip my hat to Dayton Audio because of it.
http://www.hometheatershack.com/forums/speaker-subwoofer-reviews/71766-dayton-audio-sub-1200-subwoofer-review.html
So I read this as the sub/amp combination is such that the sub will play as loud as it can, without losing it's sh!t! You can turn the volume up more, but instead of damaging anything, it will stay limited to the maximum power level it can reliably maintain.
So, if I had a SUB 1200 and the amp died (and amps are more prone to failure that speaker drivers, unless you blow the speaker with too much power), I would very much want to use the same amp!
You can probably set up an iNuke 6000 with DSP to perform similarly, but it would take some knowledge and testing that the average Joe is not going to be quick to take on, and sometimes learning by experience can be expensive.
Also, the plate amp really isn't difficult to deal with - usually 12-20 screws and 2 to 6 wire disconnects and your amp is "free" of the sub.
Here is a post from a guy who recently had an amp failure:
I recently had one of my SVS SB2000 subs stop playing and contacted SVS to see what, if anything, could be done to fix it. The sub is a few years old, but to my surprise, everything was covered under warranty. I called on a Friday morning, they had me run a few diagnostics and determined the amp was bad. By the following Wednesday, I had a replacement amp which I was able to easily swap in. No need to send the entire sub back. I paid for the amp up front, but the cost was refunded when they received the old amp back which was shipped back in the same box that the new amp came in. Shipping was also paid by SVS. I will definitely buy from them in the future.
https://forums.audioholics.com/forums/threads/hats-off-to-svs-customer-service.111075/#post-1245494
If the company you bought your sub from requires you to return the entire sub (you pay for round trip shipping) for repair without doing any troubleshooting; I feel like they are using the cost of shipping as a means to get out of their warranty claims.
While I can understand you desire for the ability to choose your amp, I think the reasons to stick with the original design far outweigh the benefit of being able to swap out your own amplification!
Edit: William's post (#9) was made while I was typing which makes mine somewhat redundant, but I did provide deeper details!
