What the guys are trying to say is that, for whatever reason, your speech engine is not able to pick up a specific word. There is zero code in VA that tries to figure out what to do with English numbers - it's all reacting to what the speech engine is interpreting. If you have 1;2;3;4;5;6;7;8;9 in a, 'Wait for spoken response' action, the speech engine is fed exactly that - 1 through 9 (numeric) and not 'one' through 'nine' (alpha). You speak, 'one', the speech engine is able to make the connection as, '1'. You speak, 'six' and the speech engine somehow is not able to make the connection, no matter what. This would be classified as an anomaly of the speech engine, and speech engine anomalies are not uncommon - it could be speaking style, it could be environment, line noise, drivers, hardware, etc. that contribute to how the speech engine behaves. The speech engine also, 'learns' over time, so that could be a factor. I would go with the suggestion of trying a new speech profile to see if that helps at all.
All that said, do you have any other commands in your profile that have the word, 'six' in them? It is possible that the speech engine could be using that to make its decisions. Try typing the word, 'six' in the box at the bottom of your profile edit screen to see if anything comes up (for grins, also try, '6'). If so, you'll want to work with that. If not, you're still at the mercy of the speech engine and will need to adjust your profile accordingly and/or create a new speech profile, as the guys are suggesting (they are long-time VA users).