Ideally you would audition the Onkyo amp vs the MF in your home (as with others you may be considering). You may be able to purchase one or both here used on Audiogon and play with them awhile and sell the one you least prefer at little to no loss. That's the beauty of Audiogon. These particular two amps have very different build designs and are likely to sound different. Not that one is "right" but one will probably sound better to you. MF is known for well made gear. Another consideration is the Onkyo has a built in phono stage which you may enjoy later should you choose to get into vinyl.
I own both the MH CD 25.2 and the Denon 2910. The 2910 is now used DVD only and the MH is in a second system. The 2910 was in the second system but my BR DVD crapped out so it was employed with the TV. I bought the MH CD 25.2 as a replacement. For the money used, just considering redbook, I prefer the 2910. Also, the 2910 will also play SACD and DVDA. I have not heard the Onkyo CD player, but it was designed to match the amp so it may be a consideration should you go with the Onkyo amp. Also, you would probably only have to deal with one remote. However, I have my doubts as to to the Onkyo player being significantly better on redbook than a 2910 just based on it's price point new.
I own both the MH CD 25.2 and the Denon 2910. The 2910 is now used DVD only and the MH is in a second system. The 2910 was in the second system but my BR DVD crapped out so it was employed with the TV. I bought the MH CD 25.2 as a replacement. For the money used, just considering redbook, I prefer the 2910. Also, the 2910 will also play SACD and DVDA. I have not heard the Onkyo CD player, but it was designed to match the amp so it may be a consideration should you go with the Onkyo amp. Also, you would probably only have to deal with one remote. However, I have my doubts as to to the Onkyo player being significantly better on redbook than a 2910 just based on it's price point new.