Need better bass from Silverline Sonata

I'm using a pair of Silverline Sonatas (model 1 with single bass driver) in a mixed HT/2-channel system. In general I'm very happy with the sound -- particularly when I get the chance to pull the Sonatas out into the room -- but I feel the bass is lacking impact and real extension. Any ideas on improving bass response without using a sub (I have a Servo-15 which is great for movies but I haven't liked the results with music)? My budget is $2,000 in addition to any resale value I get selling replaced items.

Thanks in advance for your advice.

My "2-channel" setup is as follows:
Sony S7700 to Bel Canto DAC2
analog through a Bryston SP-1 to Bryston 9BST
then the Sonatas
Cables are D-60 to the DAC, Alpha Core TQ2 to/from SP1 and Acoustic Zen Satori biwire to the speakers. I'm using Virtual Dynamics Nite power cables on the DAC, SP1 and 9BST.

Options considered so far:
- replace the I/Cs with Acoustic Zen WOWs
- replace amp with new model Bryston 4BSST or pair of Evo 200.2s as monoblocks (SET-ish sound good with Sonatas?)
- replace speakers with Totem Mani-2s
I also own the Sonatas. Unless you have a spent a good deal of time working on placment I would do that first. I consider the Sonatas to be a very difficult speaker to get just right and I have been there as far as the lack of bass you are describing. The Sonatas are capable of serious low bass, so I would guess it is more of an issue of placement than anything else. If you are looking to change amps I would check out Pass Aleph amps, they are really magic with the Sonatas.
I was thinking about buying Sonata I's. In my research,
I read that the Sonatas sound absolutely great, but are
missing bottom end extension. It was a complaint that kept coming up from owners and reviewers. Best way to get bottom end extension is to increase the power of your amp. But, the Sonatas are incredibly efficient and shouldn't need much power to make them sing. Another way to get more bass slam is from your front end components. But, rather than rely on my memory, I would get info on how the Sonatas are rated as far as bottom end extension. IMO, trying to get the Sonatas to produce bottom end extension with cables if they are not built to resolve low bass will ultimately prove frustrating. My best advice would be to either enjoy
your speakers for what they do well, which is produce wonderful music from mid-bass on up, or to add a top-notch sub-woofer, which will give you the bottom end you are seeking. Personally, I like the Revel B-15. It is
expensive, but it has an excellent set-up to help you
integrate it into your system. I see them offered used
on Audiogon from time to time.

4bsst, 2g in canada
makes my dynaudio 1.3's live well

I did some experiments, using a sunfire signature sub.
With music, I wasn't able to tell if the sub was on or not!
Made me wish I'd bought the amp first, seriously.
The soundstage goes wayyyyyyyyyyyyyyyyy back.
It made my system

sony 7000 dvd, marantz av550, dynaudio contour 1.3, 4bsst, kimber
I have Panatella II and I have a similar situation. They do wonders with mids and highs, but there low end isn't always there. I believe it has something to do with the way the speaker is built. They are very narrow and I think this is what makes the bass very compact and tight.
I agree with Rsbeck that cables probably wont give you more bass extension. However, you can affect your tonal balance to tilt the bass up a notch which might satisfy you. I've found AZ Matrix II to give that effect and Cardas Golden Reference to a somewhat smaller degree.
Same issue here- I just replaced my NHT 2.9s with Sonata 1s. The NHTs do bass really well - as well in fact, as the Sonatas do the treble and midrange.

Though I've only had them 2days, I spent most of the weekend tweaking placement. Placement makes a lot of difference. The Sonatas are capable of filling the room with bass.

I'm using a Krell KSL and a KST100, Shanling CDt200, Harmonic Technology Magic Links/Monster 2.2s with the Sonatas - the NHTs may be just a tad more 'immediate' sounding but the Sonatas have plenty of slam and are not as lean sounding as the NHTs. Bass extension will probably have to come from a sub.

Another thing - the previous owner of my speakers only played them an hour a week for the time he owned them (18 months)so, according to reviews I've read, they are not broken-in. As I played them (10 hours), the bass response became tighter and more controlled sounding. The upper bass is so powerful that I'm going to have to place tube traps in the nearest corners.
Thanks for the replies and suggestions. I ended up switching amps from the Bryston 9BST to a pair of Evo2s, which I'm using as monoblocks. Bass has improved dramatically...way more impact and more guts in the lowest ovtaves. Is it the additional 240W per channel? I don't know. Sonatas are very efficient so they shouldn't need the power. Maybe the Evo2s just have a different tonal balance from the Bryston. In any case I'm very happy. Now I need to figure out if I want to take Alan up on his offer to upgrade the tweeters and midrange drivers!