Think about it some. List off in order all the chain of stuff it has to go through, and the inherent shortcomings of each chain.
You are taking a high level amplified signal that has been through several stages, then trying to drop that signal down to line level again, then amplifying that signal yet again.
Stuff we used to do with 70s/80s car audio. There is always a loss, a gain in noise, and added complexity.
I thought this was an obvious no brainer. Maybe not.
I would only use it as a last resort if I had no preamp level line out.
I guess maybe the simplest explanation, is to question, would you do this 10 times in a row? Daisy chain 10 power amps together this way.? The answer is Hell no. For the same reason it is worse to do it just one time.
Speaking as someone who spent two decades in the car audio industry at the timeframe in discussion here- there are some significant differences, between what we are doing here, and what was commonly done in car audio ("line level adapters").
1) Car audio head unit amplifier sections, are INCREDIBLY SIGNIFICANTLY MORE NOISY than the home audio amps we are talking about.
2) Car audio line level adapters were commonly being used for FULL RANGE applications. The high-frequency hiss was MUCH more audible, than in a subwoofer application- where the low-pass filter of the sub itself, reduces the hiss by SEVERAL ORDERS OF MAGNITUDE.
3) Many car audio head units were BTL- with DC on the outputs- and the methods used to isolate from this DC in car audio line-level adapters, were far from ideal from a sonic standpoint. This also not a factor here.
Also, the argument about "daisy chain 10 power amps" is really, a fallacious reducto ad absurdum argument. No one is suggesting doing this more times than necessary- which is usually exactly ONCE.
The one thing that cannot be denied, is that there are drawbacks to any method. While the high-level input may have a very slight noise penalty- there is no denying that the low-level subwoofer input has the drawback of the subwoofer losing the correlation to the transfer function of the main amplifier. This WILL have an effect on how well the sub amp can be integrated, in phase, time and amplitude, with the main amp- usually detrimentally. It's just a matter of which approach works better in a specific system- THIS, not the purported "cheaping out" of using high-level outputs (implying that it's only because of amps not having low-level outputs), is actually the primary reason why these high-level inputs continue to exist- even on a number of very high-end subwoofers...
Regards,
Gordon.
