Would a preamp help?

I've just changed around my system completely... I went from a multichannel setup based on the Theta Casablanca to:

Theta David CD/DVD transport
dCS Purcell upsampler
dCS Delius DAC
2 x ARC VT 100 Mk IIIs
ProAc 3.8s

Cabling is Kimber Orchid AES/EBU from CD/DVD to Purcell, dual Kimber Orchid AES/EBU from Purcell to Delius, Kimber Silver Streak XLR->Kimber Silver Streak Y Splitter from Delius to amps, and dual runs of Kimber Monocle XL from the amps to the speakers. Everything is powered by DIY VH Flavor 1/2/3 PCs to a PS Audio Power Director.

I'm finding the resolution improved, but the music seems to lack some immediacy and drive--the slam factor. Bass is also a bit overblown, but I think that is attributable to room placement issues and bass I wasn't getting before.

I'm trying to figure out whether the issue is a whole slew of new cables and break-in issues--the Orchids and SS are all out of the box--or whether its the lack of a preamp. If you think a pre would help, any suggestions? I guess my immediate reaction might be to find an ARC LS25 Mk II or Ref 2 Mk II, but its a pretty expensive upgrade...
Yes, an ARC LS16mkII, 25mkII or REF2mkII would help dramatically in the drive/dynamics/life department. I'm an ARC and ProAc dealer, so I have some experience with your gear. Everytime I have tried eliminating the preamp, the result is somewhat lifeless yet transparent sound. The newest ARC preamps are so transparent that you won't get any downside to inserting them in the system. They will help control the bass better as well.

As for the boomy bass, this is a tendency of the Response 3.8 speaker. They need to be far away from walls to have a chance. Also, you need speaker wire that is fast and tight in the bass. This means no stranded wire and preferably very carefully chosen solid core wire.

The only other recommendation I can make from experience is to try a Vandersteen 2Wq subwoofer (or preferably a pair). They improve the sound of the system dramatically by removing a portion of the bass burden from the ProAcs, while also helping the amplifiers as well.

Good Luck
You might want to check out the SCE Harmonic Recovery System, a "black box" costing about $450 brand new. It follows your DAC, and connects to your amp(s) and when you "google it" you can read the reviews about how it optimizes the connection, including restoring the pace, drive, harmonic richness, and slam. Also, see similar comments here on Audiogon. It is another active device which is transparent, except for making everything better.Once you insert it into the signal chain there is never anything more to do. It just sits there, always on. They go used for about $250 here on Audiogon. I use one in each of three systems, both with, and without a preamp.
I would look for a solution before purchasing a pre...

What you describe sounds like the Delius isn't driving the amp too well -- i.e. the dac's output impedance is too high at certain frequencies. This is surprising though... what's the VT100s' input Z? I assume the Delius is 600ohm or less.
Items like the SCE mentioned above by Listener provide a "buffer" service so as to achieve a better transfer (i.e. a lower source impedance to achive better voltage transfer to the load/amps).

A pre would add another stage to yr chain. It would drive yr amps more easily at the expense of some resolution (unless you go for the exotic, i.e. Blowtorch, & the like).
Thanks for the responses... I'll google SCE.

The dCS website sez the Delius output Z is 1 ohm... According to the ARC website, the VT100 has an input Z of 200 k ohms for the balanced inputs, 100 k for SE; I'm using balanced.

Hmm... Does the fact that I'm using a Y splitter off the dCS output alter the normal compatibility concerns?

I'm also going to have to check my Delius; reading the website just now, it appears the output is selectable 2V or 6V via software, and I'm not sure where its set--I'm assuming 2V is the right #. If it was set at 6V, would that explain anything? Given the #s, it doesn't seem like the Delius output Z could be construed as too high...
You may also try some kind of a buffer instead of preamp if you don't need a volume control on it directly. I think bvaudio has something like that called sound refiner, check their website.
Thanks for the input. I guess I may pull the LS16 out of another system and see what happens...
Edesilva: if you're riving two 200kOhm loads in parallel, the Delius is looking at an equivalent 100k load -- a very easy /trivial load for a 1ohm output Z device...
If you can set the delius to 6V output do so -- you might be feeding insufficient voltage into yr amps.

Generally speaking, with 1ohm output (more or less across the AF band, right? -- or is it 1ohm only at 1kHz?) you certainly don't need another pre (yr Delius already includes one pre)!