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