Looking to polish off my rig

I just got the Little Dot MKII for my DT990 600Ω, and I'm amazed at just how much soundstage this thing has when properly amped.  I assume it even gets better the more I scale up.  For right now I'm just looking for possible upgrades to the stock tubes and eventually maybe a dac as well.

I heard the EF92 Mullard drivers are very good over the Little Dot MKII's stock tubes.  What I'm looking mainly for in the driver tubes would be a bass that extends lower and/or is tighter with possibly more impact, and even wider soundstage (can't get enough of it!).

I actually don't mind the treble and the recessed mids too much on the DT990.  Power tubes might be an option as well, but from what I understand they don't do as much as driver tubes.  I wouldn't mind power tube recommendations as well though.

As for a dac, my main candidate so far is the HRT Music Streamer II, are there any alternatives that are just as good as it that might warmer in signature for around 150usd?

As an update, I now have the HRT Music Streamer II as part of my rig, but I'm still looking at upgrading my stock tubes.

Are these the right type of tubes I should be looking at? I'm wanting some M8161 EF92 Mullard driver tubes, but I don't see the usual mullard logo on these.

http://cgi.ebay.com/Matched-pair-Mullard-CV4015-M8161-tubes-MILspec-EF92-/380338389576?_trksid=p4340.m263&_trkparms=algo%3DSIC%26its%3DI%252BC%26itu%3DUCI%252BIA%252BUA%252BFICS%252BUFI%26otn%3D10%26pmod%3D260771530612%26ps%3D63%26clkid%3D9037830156063002154#ht_2568wt_733

Are there any other driver tubes I should be looking at for my Little Dot MKII?  Main thing I'm looking for is more sub-bass impact, because as of right now, the real lows seem to be a bit rolled off: 40-50hz seems to be nice and strong, but 20-30hz seems to be very weak.

When I first got it and hooked it up, I was very amazed at just how efficient at made my amp, without having to double amp off the computer anymore-- plus the added benefits of having higher signal-noise ratio and no interruptions of music playback form computer tasks.

At first the soundstage seemed to be really congested, but I think it's since then cleared up.  Mids definitely seem more thick, and there is a slight boost in bass impact.  I can't comment on much else, in order to truly a/b it vs the computer's audio, I gotta get used to it and then switch back to see what I got spoiled off of.

Anybody else for tube suggestions?