For frame of reference, I began w/ a full-up RWA version of the SB2+battery PS, had it bested by Wayne's 'Basic' mods and PS, and finally had the 'Basic' absolutely trounced by the 'Ultimate' PS and additional SB2 mods. Consequently, the comments to follow are in reference to using the 'Ultimate' PS and my latest addition, a Maui Mods/Aberdeen Components Transporter.
In my system, every addition I've tried so far - be it a preamp, or even a power conditioner - has resulted in some sort of degradation in the sound. The 'Ultimate' PS immediately took care of any perceived thinness I heard w/ the 'Basic' PS, and my experience w/ the modified Transporter is the same. Far be it for me or anyone else to claim to have a definitive answer, but my initial thought is that you may want to give the 'Ultimate' PS or a Maui Mods/Aberdeen Components Transporter a listen.
Point being, it sounds like your system is resolving enough to highlight the limits of your current mods, and it may be necessary to either add a preamp back into the chain or change your current mod configuration to get the musicality you seek. IME, going direct to my amps w/ a fully modified Transporter or 'Ultimate' PS gave me the air and spaciousness you heard, but with the fullness and organic presence you seek.
We all have different things we seek from our systems, and it may be that your desire for fullness or warmth or whatever is more than any mods can offer. In that case, a preamp is probably your best bet. Even so, I'd definitely try a full-up version of
something else before deciding to add another component into the chain. Once you hear the clarity and air a direct connection offers, it's awfully hard to go back. In my case, it's proven problematic in that I'd like to have more than one source, but I've yet to find a pre- that doesn't rob me from some aspect I've become accustomed to hearing. Consequently, until I find a preamp I can't hear, my system will remain single-source.
Given the quality that single source produces, I'm OK with that.
Obviously other system components (amp(s), cabling, speakers) have a profound impact on what you hear, too, but I really think you should consider trying something almost universally accepted by everyone who's heard it ('Ultimate' PS) before changing anything else.
Hope that helps, even if it's just a little.
Take care,
-Jim