I tend to agree with GSophile, it seems we should be able to appreciate the improvements within the range we do hear.
The dealer should be willing to put his DAC where your money is, I mean, have him lend you something so you can hear a comparison. That's the only way you will know. Or, if the dealer has your preamp go in and do some listening, experimenting.
In my case the 526 is a very good preamp, they included a capable DAC. In my opinion it should have been better. I ended up spending the money for an external DAC. Now McIntosh may have an entirely different allocation of expense to go into the preamp and included an excellent DAC. In, addition, I fully believe in having the best source I can. Others feel any ole DAC will do, 1's & 0's etc.
Hope my rambling helped some, LOL
With all that being said you may be satisfied where you are at and not interested in spending more money no matter the result.