image of MX 170 from Sennheiser.com
A comparison between MX 170 and 375
First impression is that these are really good value. They do indeed have good bass for their size. They do sound a little bit muffled but sometimes this a good thing.
This might be due to different frequency response of 22-20,000Hz. The next model up might (MX 375) have better higher frequency responses I suspect. Just checking, yes it does 18-22,000 Hz.
In comparison to PXC-250 II noise cancelling over ear style the higher frequencies are a bit better brighter.
Update
image of the MX 375 from Sennheiser.com
Now testing out the MX 375. I have to say these are much more even sounding, not too bassy and higher frequencies are well reproduced. Good bass but not anywhere near as muffled as the MX 170. These definitely produce a nice replication of the style of sound I prefer.
Which should I get? the MX 170 or MX 375?
The style of music is also significant for your choice. If you listen to a wide range such as classic with subtle sounds the MX 375 are the better choice. The MX 170 are probably good for popular bass sounds of current charts. Listening to video narrations such as Attenborough sound better on the 375 model too. The price difference is not that much either. MX 375 is about $A10 more.