which one of those two you recommended would you buy
Doesn't matter - they're essentially the same router (except one has a USB port, in addition to the ethernet port). Both have the same DSL chipset (which is the important thing).
Also remember newer firmware versions either don't support DMT at all, or offer much reduced functionality via DMT.
As the firmware versions got newer, the DMT functionality decreased (first the bitloading and SNR graphs disappeared, then the SNR tweak was removed).
If you get a v7 you'll probably find nothing you're interested in works on DMT.
The 536v5 is still available from DSL depot ('b' grade version for �10.99), and the 546 is available in v5 and v6 versions (99p more for a v6).
Hm why not the 510v6
Simply because it's not listed on the DMT site as being compatible (so it's either got a slightly different chipset, or doesn't exist in Germany).
Ade
ADSL24/Entanet - 22 months and counting, with Entanet!
DL Sync 4000kbps
UL Sync 448