DAC recommendation?

Bryston 4B Amp
Bryston 11B Preamp
Krell CD-DSP
Thiel CS 3.5 Speakers

My system is over 20 years old, and I was hoping to get recommendations for DAC and any other modifications or replacements to get best "bang for buck". Planning on running a Sonos ZP-80 through this system in addition to the existing Krell CD player. Power supply? Cables?
Check out Cullen Circuits for his moded ZP 80 and moded PS audio DAC III
Always a question of know much you want to spend.I have owned Bryston and sold Krell for 6 years.Good thing Krell you have is CD because like all Krell is brittle and clinical but will be fine transport.If you want to spend short money try the Benchmark.6moons.com had review of anther $1K PS Audio DAC with extra mods that they say is benchmark for price.A bit more Eletrocopniaet.But I think if into computer audio now or adding in future you could look at Slim Devices Transporter,have DAC,computer audio and even take pre out of occassion.Getting up on learning curve isn't as hard as you think.

As far as rest of system Bryston is great with some speaker.Perfect combo with my buddies Maggies.But the new SST series is expensive.Looking for a 4 B ST where design took great leap forward is the one really good used value if you can find later model with 10 years on 20 year warranty for $1250-$1500.But for another $500 used you could get 500 Watts from & ST mono's or 1`4 ST amps.But now wy not if possible (since I think SST series of Bryston is close in sound to ST the one after yours) a/B with them with something getting good press like the Class D amps like Bel Canto or PS Audio that are getting good press.You want precise,corect harmonic source of course but after speaker design amplification should have the character and pre be t neutral gate though I don't like passive controllers do to lack of bass and dynamics.I bough a buddy a pair of Thiel CS 7's but was underwhelmed (should have gotten next 7 model with their own drivers).I hear 3.6's are fine but bests in thier series were CS 6.Get any DAC you can afford by asking questions here or Audioaslylum but if you can swing it best source though not cheap is Modwright modded Sony $4K deck.Even the stock one would amaze you compared to what you have.After 20 years caps dry out,surrounds degrade and if you can afford it do reading and asking and replace piece by piece.I'd leave pre and amp till last change.But each piece will pay off.Even though I sold and used high end cables (Cardas were great for "softening" Krell for friends even though boss carries other brands.Some that were expensive like MIT rolled off frequency extremes,accentuated mids and made people "think" they were better but it was just less sound).Kimber,Cardas don't spend a a lot.Zonos sounds fine though.I have used 20 Guage Home depot copper on freinds systems and it was fine.AC conditioning,or filering depends on where you live and how much garbage in signal.Both like nice ,heavy (I like Sound Anchors heavy iron mass with cone/points) are all frosting on cake off a good stereo chain of speakers,amp,and pre,source (I reverse it in importance,but believe keeping it equal in price/quality).
Like us all cash,time,access to stores with right goods gives us opportunities others do or don't have.Have fun in the hunt.
I almost never say this, but you might want to upgrade to the newer SST versions of the Bryston electronics. I owned the 7B SSTs for 5 years and still use the BP26 preamp. I've never heard the older models, but many people say the newer versions are smoother sounding.

I use a Benchmark DAC1 and I think it's a great product. I've also heard a Lavry DA10 in my system and would not hesitate to recommend it.

I think for almost every system a properly setup subwoofer offers the absolute biggest bang for the buck. Thiel subs are quite expensive, but there are suitable alternatives for a lot less money.
Please consider April Music stello DA100 Signature DAC. It is compatible to most of modern digital interfaces including I2S and has full balanced and unbalanced output circuits with discrete devices. Many people are using for Sonos and PC as digital sources with excellent results.

April Music USA