Thoughts on a Marantz MM9000 amp for a 4 Ohm ...

speaker. I have the MM9000 which is rated at 150wpc into 8 Ohms. The spec sheet doesn't mention powering speakers with lower nominal impedence. I'm purchasing some Dynaudio 1.8s (4 Ohm) and I'm not in the mood to upgrade my amp just yet. Will this amp put my new Dyns at risk?

No, the amp itself would be the one at risk. But, most amps can drive a 4ohm load easily and it should supply more power into the lower impedence. Look on the back of the amp next to the binding posts and see if it says anything about speaker impedence. If your still not sure, contact Marantz.
Dynaudio's require gobs of power to perform at their best. While your amp may be able to drive them to very reasonable listening levels, your speakers will not be doing what they are capable of providing until you can provide them with both a higher quality and quantity of signal. In the meantime, use the Marantz and see how you like it. It may work out just fine for you. What each of us expects out of a system can be very different things. Sean