I don't know why the question asked is not being answered here. The question seemed to ask how to get the best bass out of an SSE. I will answer that, but I need to explain a few things. Just stating that "you need a subwoofer" without explanation is not a valid answer, even though it may be a valid choice.
High power, ultra-low frequency audio's higher power can easily damage your excellent drivers, ... but if the ultra-low part is removed, and separately amplified ... then your main audio speakers are saved
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I highly doubt that an SSE can damage either of your speaker systems no matter how you run it. A solid state amplifier run into clipping will produce a lot of high frequency energy which can blow tweeters. This is not the case with most tube amps. Woofers are usually blown from long term thermal damage, or overexcursion of the cone, both come from too much power, either tube or solid state. An SSE does not have too much power for either of these speakers.
Vacuum-tube amplifiers are famous for being unable to attain high-power low-frequency audio without remarkably excess money.
I can demonstrate several reasonably priced tube amps capable of high power at low frequency. I have one under development that makes 300 watts at 20 Hz. There are two reasons for a blanket statement like this, and cost is involved, but this statement is not entirely true. There are two reasons that many tube amps are weak in the bass region.
Most tube amps use an output transformer to transform the audio signal from the high impedance tubes to a low impedance needed to drive the speaker. The low frequency response of this transformer is directly related to its physical size, and therefore it's cost. An SSE with the right OPT can produce full power at 20 Hz without saturation distortion. The EDCOR XSE15-8-5K may not be the right choice for the JBL clones.
Many tube amps, and most SE tube amps do not use negative feedback. Negative feedback will lower the distortion, and increase the Damping Factor of the amp. Too much feedback tends to suck the life out of the music. Most SE amp users prefer no feedback at all. Some speaker systems need a relatively high Damping Factor for well controlled bass. Dynamic sounds like the kick drum hit can sound "loose" on some speaker systems with an underdamped amp. The AN speaker was designed for these types of amps, but the JBL clones were made for a solid state amp with a good DF. The DF of an SE amp is relatively low. The tube choice will affect it. So does the idle current, and the OPT.
I have an SSE with exactly the same components that you specified. I run it with Yamaha NS-10M Studio monitors which have limited bass below 70 Hz, so I use a subwoofer. The little Edcor XSE-15-8-5K OPT's begin to roll off the low frequencies below about 90Hz so I have the sub's LPF set to 120 Hz. It is a cheap 10 inch amplified speaker box that claims 100 watts, but it does the job perfectly in a 10 X 12 foot room. I don't try to play this system very loud, but it does do OK with anything I feed it. I am building a bigger sub using a Parts Express 15 inch driver and 300 watt plate amp. The bigger system is not to get louder, it's to get lower since I have been playing with a music synthesizer.
I have another SSE that uses the larger CXSE-25-8-5K transformers playing through a home built set of speakers that use 15 inch woofers with 96db efficiency. There is NO subwoofers, but the bass from this SSE can be felt INSIDE the HOUSE ACROSS THE STREET! This SSE can produce 15 watts from 20 Hz to 18 KHz. NO SUB NEEDED, or wanted.
In this case the Electro Harmonix KT88 or 6550 tube produces the best most well controlled bass and power. I use UL mode with the CFB turned on. Pink Floyd, Depeche Mode, Metallica, all sound great at high volumes. The 6L6GC doesn't have the solid bass, but is a good all round performer. I use the EL34 in triode with no feedback for the best detail with female vocals. It still shakes the walls in my house, but not the neighbors, since it only makes 6 watts.
An "8 ohm" speaker is usually not 8 ohms. It should be close to 8 ohms at 1KHz and will vary all over the place at other frequencies. It will go way up, maybe 20 to 100 ohms at the resonant frequency of the woofer, and be quite low below this frequency. Most modern audiophile quality speakers publish this curve. The small Edcor will start to saturate (distort) at anout 80 Hz with a true 8 ohm load at 10 to 15 watts. It will go lower at higher impedances.
You already have the small Edcors, so I would try them. They should be Ok with the AN's. There is a chance that the impedance curves of the JBL clones will allow the small OPT's to produce reasonable bass. There is also a chance that they will not. If the speaker's impedance goes up in the region where the OPT starts to saturate, then things can work. If the speaker's impedance remains flat, or drops, then the bass can sound weak or distorted.
if the bass is not good enough with the small OPT's, then the larger Edcors or a subwoofer system can be considered.
If you do think about a sub, then you want one that uses a line level input, and has a built in LPF. Avoid anything that connects to the speaker leads when using a tube amp for the main speakers. Connecting it as the Goat Guy says (across the SSE inputs) usually works the best, and is the way I have mine wired. There are several other SSE builders who have used the small Edcor OPT's with a sub and a full range driver like the AN, or Lowthers.
