The Acurus can probably be improved upon. You didn't give us a budjet to work with. As a generic answer I like what tubes do a lot and have them in almost every place I can. What sound are you aiming for? An older ARC piece may be affordable to you, they typically clean up your sound, as they say precision instruments or something like that. If you want a little more warmth an old Conrad Johson or even a Cary. I like the Cary because he uses 6SN7s in his (tube) designs.
Sorry, I should have mentioned I am budgeting around $2500.00.
Based on reading about the DNA 0.5, & having one in one of my systems (with Spendor S3/5 SE's), I'd keep the McCormack--very nice sounding amp, unless you have very hard-to-drive speakers perhaps.
PS--what are you looking to do, i.e. what's bugging you about the sound now, etc, that you want to improve?
I have no first hand knowledge of Spendor speakers, but I recall reading a review on Musical Fidelity's current M6 product line that specifically mentioned a couple of speakers that pair very well with M6 components. One of the speakers mentioned was the Spendor S9, so to the extent that the A5 may have similar characteristics to the S9, then the Musical Fidelty M6PRX amplifier would probably be a good pairing. The review I am referring to was by Alan Sircom and published at avguide.com.
I use the M6PRX with B&W 804 Diamonds, which is a combination that I like although it is not one that Sircom mentioned. I suspect a used M6PRX would be in the vicinity of $2500 or perhaps a little bit more. It's an outstanding amp that you don't hear much about, which is a little surprising given several absolutely glowing reviews.
The only caution I have about the M6PRX is that does run on the warm side so it's definitely not an amp that I would place inside any kind of cabinet.
A possible upgrade for your McCormack DNA .5 is to try and score a used DNA .5 that has been upgraded by SMc Audio. Sometimes you can find them here on A'gon for about $900- $1000+. If not you can send it to SMc Audio for mods. Whenever I've spoken to Kris or Steve they always are willing to customize the mods to your needs and give you the most for your buck. To me if you are happy with the McCormack just stay along those lines.
Steveaudio: Actually, I have no issues with the sound of my system, just that I have had the McCormack and the Acurus pre amp for 13 years and I'm itching to try tubes!
You should go ahead and do that then. The Spendors have usually been tube-friendly.
*Actually, I have no issues with the sound of my system, just that I have had the McCormack and the Acurus pre amp for 13 years and I'm itching to try tubes!*
Easiest thing: Get a tube pre-amp. Like Mechans said, a used ARC, C-J, or Cary, you could add VTL. I have a wonderful Cary SLP-98 pre-amp, but paired with a SS (C-J) amp. Depending on what kind of sound you want, you can get some pretty nice used tube pre's for $1000-ish. Want kind of "tubey"? A VTL 2.5TL, or older C-J. Pay more, like for a more modern C-J or Cary, that's a different sound. "Better", more neutral, but still will add some "tube warmth".
Tube Power amps: that's a whole 'nother issue. Make sure your speakers are fairly efficient, & "tube-friendly". I'd start with a tube pre......
IMHO, the Acurus is the weak link, and though not because of that, the least tube like sounding component in your system. It would seem that the Acurus would be the component to consider replacing with a tube unit. But a bit of caution might be in order. I can't seem to find the specs on the DNA .05, but different models of McCormack amps had various input impedance's and sensitivity. Some had input impedance's that might be a bit low for some high output impedance tube pres, and others had a rather high sensitivity for some of the tube pres that have higher output, compromising the usability of the pre volume pot. Using a tube pre can work, and work well, but as always do your homework first.
I agree that the McCormack is the week link if looking for a tube sound, I also agree that the pre's mentioned are all nice sounding tubes and that the DNA.05 is a fine sounding amp, BUT, if you are truly trying to add a tube flavor to your system, no preamp will add near the flavor of a good tubed amp. So be prepared that if you take a preamp suggestion, it might or might not be "enough" of that tube flavor that you are looking for.
I agree with Timlub's sentiments. But just getting a tubed pre-amp can be a very fruitful venture and worth the effort. Getting a tubed amp can come latter after you've figured out the tubed pre-amp issues (it is wonderful to be able to adjust tonal issues etc by simply changing tubes). You may never need a tubed amp. Some folks like the sonic merits of SS so the combo can be a good compromise. But be careful, some tubed pre-amps sound pretty much like SS, especially tonally speaking. You might do well with a vintage tubed pre if you want to stop with a tubed/ss combo.
FWIW, if I had to, I'd probably get a high quality SS pre-amp and a vintage tubed amp. But I rarely will recommend it because there is a learning curve and maintenance issues with tubed amps you must be ready to deal with, not so much with tubed pre-amps.
Very good advice from Steveaudio. But it's vital that you match the impedance levels. The tube preamp output impedance must be low. (Many of the newer tube pre's have low outputs).