Musical Subwoofer for 2 Channel System BUT....

I have an integrated amplifier (Karan Acoustics i180) with no sub out: only inputs and the speaker posts.

Does anyone have a suggestion for a great musical sub that would work with this setup? I am looking to spend under $1000, new or used, and the amp is paired with KEF Reference 1 speakers. Oh, and I listen to a wide range of music, but tend toward Blues, Jazz, and female vocalists (e.g., Nina Simone, Natalie Merchant, Margo Timmons).

Thanks, really, for any help.
Rel S series work best (IMO) when connected to speaker outputs. I have a Storm III, and Storm I; both very musical. Search on "Rel" and you'll find many many endorsement of the Rel Strata III and Storm III. the Strata III can be found used for under $1000, the Storm III may cost a little more than $1000.
Thanks. Everyone seems to love the REL's. I have not seen one up close yet, but from the picture I'm looking at I can't tell if the inputs are speaker level or line (pre-out). I am sure based on Bdgregory's post that they accept speaker wire input, though I'm not sure b/c I know there is a way to convert a speaker out to a line out. Could someone please confirm that these inputs accept speaker wire? Thanks.
Ok. A little more research and I found my answer on the REL website:

A. It is helpful to know that you will almost always connect the REL to the input on the rear panel labelled "Hi Level." This connection is made using the supplied cable, the bare leads of which connect to the speaker output terminals of the power amplifier (red to the amplifier’s primary right speaker red terminal, yellow to the amplifier’s primary left speaker red terminal and black to one of amplifier’s primary speaker black terminals (not both)). The easy connection at the REL is completed with a Neutrik Speakon connector. The purpose of connecting to the speaker output terminals is one of the unique secrets of REL’s success. By connecting to the REL’s High Level input from the amplifier, you build forward the sonic signature of your main system, including the tonal balance and timing cues. In this way, the REL shares the signal that is fed to the main speakers.
Here's a few more for you to consider

ACI FORCE And Titan Subs

Adire Rava II

Acoustic Vision MRS-10


Acoustic vision Subwoofer Complete Kits series

TBI subwoofers

Rocket UFW-10 Subwoofer

VR-S/1 High-speed MiniSub personally I think the Q is too high on this sub. Thought I would list it anyway.

Here's a website that may help you along the way

I just wanted you to know there are other great subs out there besides Rel.

Good luck

Gmood1 -- thanks for the added choices.
I was wondering if there were any opinions on Soliloquy's S-10 sub?
I use the Karan Kai-180 to drive my Quad 988's with a pair of Rega Vulcan subwoofers.The subs hook up similiar to the Rels(speakon connectors that take the signal from the Karan binding post).I feel that this is the best way to hook up subs.
I have to second the ACI suggestion.
Any used Titan or newer models is a great deal and incredible value.
I have upgraded my system countless times the past 6 years and the ACI Titan sub hasn't budged.