Which of these preamps should I get?

Rotel amplifiers are a decent amp for the money. With what might be an overly light or bright speaker, a Rotel amp can compensate by giving a slightly rich and warm overall presentation.

As for the McCormack DNA 0.5? This is somewhat of a legendary amplifier. Several years ago, the DNA 0.5 was rated a competitive second to the highly touted $30,000 Krell Reference Standard amplifier. (I believe the DNA 0.5 sold new for less than $2k.)

The McCormack DNA-2 Limited Anniversary Edition was rated the best solid state amplifier by Peter Moncrief of IAR in 1998 and according to Mr. Moncrief, the LAE easily exceeds both the Krell and the DNA 0.5 but was substantially more expensive than the 0.5. (BTW, some place Mr. Moncrief head and shoulders over most other reviewers.)

A DNA-2 Revision A or a DNA 0.5 Revision A easily exceeds the performance of the off-the-shelf DNA-2 Limited Anniversary Edition.

In summary, the DNA 0.5 amp could be a very wise choice. A DNA 0.5 Revision A amp could be an even wiser choice.

-IMO

If you decide to go Rotel way, skip RC-1070 and go for RC-1090 (new or used) or for used RC-995. I had purchased Rc-1070 and decided to upgrade after several days.

What do you guys think about the Acurus amplifiers? A250?

I'm considering buying the Mccormack DNA 0.5, but the A250 for $100 less would give me more power. Or would I lose too much quality?

The quality of the power should most always be the first priority. Not the quantity.

-IMO